Multi-piece solid golf ball

ABSTRACT

In a multi-piece solid golf ball having a core, envelope layer, intermediate layer and cover, the core is formed primarily of a base rubber, the core has a diameter of at least 30 mm, the envelope layer is formed as two layers—an inner layer and an outer layer, and the intermediate layer and the cover are each formed as single layers of a resin material. The core and the respective layer-encased spheres have surface hardnesses which satisfy specific relationships, the Shore C hardness value obtained by subtracting the core center hardness from the core surface hardness is 16 or more, and certain layers have respective thicknesses which satisfy specific conditions. This ball achieves a good distance on full shots both with a driver and with irons, is superior in the short game, and moreover has a good feel at impact and an excellent scuff resistance.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2021-035283 filed in Japan on Mar. 5, 2021, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a multi-piece solid golf ball composed of five or more layers, including a core, an inner envelope layer, an outer envelope layer, an intermediate layer and a cover.

BACKGROUND ART

A variety of golf balls have hitherto been developed for professional golfers and skilled amateurs. Of these, multi-piece solid golf balls having an optimized hardness relationship among the layers encasing the core are in widespread use because they provide both a superior distance performance in the high head-speed range and also a good controllability on iron shots and approach shots. Given that not only the flight performance but also the feel of the ball at impact and the spin rate of the ball after being struck by a club strongly influence control of the ball, optimizing the thicknesses and hardnesses of the golf ball layers in order to achieve the best possible feel and spin rate is also an important topic in golf ball development. In addition, because there exists a desire for golf balls, when repeatedly hit with various clubs, to have a good durability to repeated impact and for the scuffing observed at the ball surface to be suppressed (increased scuff resistance), maximal protection of the ball from external factors is yet another important topic in golf ball development.

Examples of such literature include JP-A 2008-149131, JP-A 2009-095358, JP-A 2009-095364, JP-A 2009-095365, JP-A 2009-095369, JP-A 2016-101254, JP-A 2016-101256, U.S. Published Patent Application No. 2009/0170634, U.S. Published Patent Application No. 2012/0129630, U.S. Published Patent Application No. 2013/0012338, U.S. Published Patent Application No. 2015/0251058, U.S. Published Patent Application No. 2015/0314169, U.S. Published Patent Application No. 2016/0317873, U.S. Published Patent Application No. 2017/0340925, U.S. Published Patent Application No. 2017/0361171, U.S. Published Patent Application No. 2018/0015332, U.S. Published Patent Application No. 2018/0008867, U.S. Published Patent Application No. 2018/0078826, U.S. Published Patent Application No. 2019/0344127, and U.S. Published Patent Application No. 2020/0086177. These disclosures, all of which relate to golf balls having a multilayer construction of four or more layers, focus on, for example, the surface hardnesses of the respective layers—namely, the core, the envelope layer, the intermediate layer and the cover (outermost layer), the relationship between the ball diameter and the core diameter, and the core hardness profile. Moreover, some of the foregoing disclosures relate to golf balls which have a ball construction of five layers wherein the core is encased by four layers—an inner envelope layer, an outer envelope layer, an intermediate layer and a cover (outermost layer), and which have specifically defined hardness relationships and thickness relationships among these layers.

However, there remains room for improvement in optimizing the core hardness profile and the thickness relationships among the various layers in these prior-art golf balls. That is, when these golf balls are played by amateur golfers whose head speeds are not high, a fully satisfactory distance cannot be achieved, particularly on full shots taken with a utility club or an iron. Moreover, with some of these prior-art golf balls, when an attempt is made to achieve a superior distance performance even on iron shots, a sufficiently high spin rate cannot be obtained on approach shots, resulting in a ball that lacks a high playability or that has a poor feel at impact on full shots. Accordingly, there exists a desire for the development of a golf ball for amateur golfers which has an improved flight on full shots with a utility club or an iron, has a soft and good feel on all full shots, and also has a high playability in the short game.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a multi-piece solid golf ball which, along with achieving a satisfactory distance on full shots not only with a driver (W#1) but also with long and middle irons, is highly receptive to spin on approach shots and thus superior in the short game, and also has a good feel at impact and an excellent scuff resistance.

As a result of intensive investigations, I have discovered, with regard to golf balls having a core, an envelope layer, an intermediate layer and a cover, that certain desirable effects can be achieved by fabricating multi-piece solid golf balls in which the core is formed primarily of a base rubber as one or more layer; the core as a whole has a diameter of at least 30 mm; the envelope layer is formed as two layers—an inner envelope layer and an outer envelope layer; the intermediate layer and the cover are both formed as single layers of a resin material; the core and the respective layer-encased spheres have surface hardnesses which together satisfy the following condition in which the hardnesses are Shore C hardness values:

-   -   core surface hardness<surface hardness of inner envelope         layer-encased sphere<surface hardness of outer envelope         layer-encased sphere<surface hardness of intermediate         layer-encased sphere>ball surface hardness;         the Shore C hardness value obtained by subtracting the core         center hardness from the core surface hardness is 16 or more;         and the envelope layer, the intermediate layer and the cover         have respective thicknesses which satisfy the following two         conditions:     -   cover thickness<intermediate layer thickness, and     -   outer envelope layer thickness<inner envelope layer thickness.         That is, an even further reduction in the spin rate on shots         with a driver (W#1) and with various irons can be achieved while         maintaining a high initial velocity when hit, as a result of         which a good distance can be attained. In addition, the spin         rate on approach shots in the short game is optimized, providing         a higher controllability, and a good scuff resistance can be         obtained.

Accordingly, the invention provides a multi-piece solid golf ball having a core, an envelope layer, an intermediate layer and a cover, the core being formed primarily of a base rubber as one or more layer, the core as a whole having a diameter of at least 30 mm, the envelope layer being formed as two layers—an inner envelope layer and an outer envelope layer, and the intermediate layer and the cover each being formed as single layers of a resin material. In the golf ball of the invention, the core has a surface hardness, the sphere obtained by encasing the core with the inner envelope layer (inner envelope layer-encased sphere) has a surface hardness, the sphere obtained by encasing the inner envelope layer-encased sphere with the outer envelope layer (outer envelope layer-encased sphere) has a surface hardness, the sphere obtained by encasing the outer envelope layer-encased sphere with the intermediate layer (intermediate layer-encased sphere) has a surface hardness and the ball has a surface hardness which together satisfy the following condition in which the hardnesses are Shore C hardness values:

-   -   core surface hardness<surface hardness of inner envelope         layer-encased sphere<surface hardness of outer envelope         layer-encased sphere<surface hardness of intermediate         layer-encased sphere>ball surface hardness.         Also, the Shore C hardness value obtained by subtracting the         core center hardness from the core surface hardness is 16 or         more. In addition, the envelope layer, the intermediate layer         and the cover have respective thicknesses which satisfy the         following two conditions:     -   cover thickness<intermediate layer thickness, and     -   outer envelope layer thickness<inner envelope layer thickness.

In a preferred embodiment of the golf ball according to the present invention, the core center hardness (Cc), core surface hardness (Cs) and the hardness at a midpoint between the core surface and the core center (Cm) satisfy the condition:

(Cs−Cm)/(Cm−Cc)≥1.5.

In another preferred embodiment, the golf ball satisfies the condition:

0.4≤(OE vh+IE vh)/Core vh≤1.1,

wherein Core vh is the volume (mm³) of the core multiplied by the Shore C hardness at a midpoint between the core surface and the core center (Cm), IE vh is the volume (mm³) of the inner envelope layer multiplied by the Shore C hardness at the surface of the inner envelope layer-encased sphere, and OE vh is the volume (mm³) of the outer envelope layer multiplied by the Shore C hardness at the surface of the outer envelope layer-encased sphere.

In yet another preferred embodiment, letting CL1 be the coefficient of lift at a Reynolds number of 80,000 and a spin rate of 2,000 rpm and CL2 be the coefficient of lift at a Reynolds number of 70,000 and a spin rate of 1,900 rpm, the ball satisfies the following condition:

0.900≤CL2/CL1.

In still another preferred embodiment, letting CL3 be the coefficient of lift at a Reynolds number of 200,000 and a spin rate of 2,500 rpm and CL4 be the coefficient of lift at a Reynolds number of 120,000 and a spin rate of 2,250 rpm, the ball satisfies the following condition:

1.250≤CL4/CL3≤1.300.

In a further preferred embodiment, the cover has a surface with from 323 to 380 dimples arranged thereon.

ADVANTAGEOUS EFFECTS OF THE INVENTION

The multi-piece solid golf ball of the invention, along with achieving a satisfactory distance on full shots not only with a driver (W#1) but also with various irons, is highly receptive to spin on approach shots and thus superior in the short game. Moreover, it has a good feel at impact and an excellent scuff resistance. Such qualities make this ball highly useful as a golf ball for professional golfers and skilled amateurs.

BRIEF DESCRIPTION OF THE DIAGRAMS

FIG. 1 is a schematic cross-sectional view of the multi-piece solid golf ball (5-layer structure) according to the invention.

FIGS. 2A and 2B are, respectively, a top view and a side view of the exterior of a golf ball showing the arrangement (pattern) of dimples common to all of the Examples and Comparative Examples described herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the appended diagrams.

Referring to FIG. 1, the multi-piece solid golf ball of the invention is a golf ball G having five or more layers, including a core 1, an envelope layer 2 made of two layers (inner envelope layer 2 a and outer envelope layer 2 b) that encases the core 1, an intermediate layer 3 that encases the envelope layers, and a cover 4 that encases the intermediate layer 3. Numerous dimples D are generally formed on the surface of the cover 4. Although not shown in the diagram, a coating layer is generally applied onto the surface of the cover 4. Apart from the coating layer, the cover 4 is positioned as the outermost layer in the layered structure of the golf ball. The core 1 is not limited to a single layer and may be formed of a plurality of two or more layers.

The core has a diameter of at least 30.0 mm. The diameter is preferably at least 31.4 mm, and more preferably at least 32.0 mm. The diameter upper limit is preferably not more than 35.0 mm, more preferably not more than 34.2 mm, and even more preferably not more than 33.5 mm. When the core diameter is too large, the spin rate on full shots with a driver (W#1) or an iron may rise, as a result of which the desired distance may not be achieved. On the other hand, when the core diameter is too small, the initial velocity of the ball may decrease, as a result of which a good distance may not be achieved.

The core has a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which, although not particularly limited, is preferably at least 3.0 mm, more preferably at least 3.2 mm, and even more preferably at least 3.5 mm. The core deflection upper limit is preferably 5.5 mm or less, more preferably 5.3 mm or less, and even more preferably 5.0 mm or less. When the core deflection is too small, i.e., when the core is too hard, the spin rate of the ball may rise excessively, resulting in a poor distance, or the feel at impact may be too hard. On the other hand, when the core deflection is too large, i.e., when the core is too soft, the ball rebound may be too low, resulting in a poor distance, the feel at impact may be too soft, or the durability to cracking on repeated impact may worsen.

The core consists of one or more layer of a vulcanized rubber composition made up primarily of a rubber material, and is preferably formed of a single layer. If the core material is not a rubber material, the rebound may be too low and the ball may fail to travel a good distance. Also, when the core is composed of a plurality of layers, upon repeated impact, the ball may end up cracking early from the core interface. The rubber composition of the core is typically obtained by using a base rubber as the primary ingredient and compounding with this a co-crosslinking agent, a crosslinking initiator, an inert filler, an organosulfur compound and the like.

It is preferable to use a polybutadiene as the base rubber. Commercial products may be used as the polybutadiene. Illustrative examples include BR01, BR51 and BR730 (from JSR Corporation). The proportion of polybutadiene within the base rubber is preferably at least 60 wt %, and more preferably at least 80 wt %. Rubber ingredients other than the above polybutadienes may be included in the base rubber, provided that doing so does not detract from the advantageous effects of the invention. Examples of rubber ingredients other than the above polybutadienes include other polybutadienes and also other diene rubbers, such as styrene-butadiene rubbers, natural rubbers, isoprene rubbers and ethylene-propylene-diene rubbers.

The co-crosslinking agent is an α,β-unsaturated carboxylic acid and/or a metal salt thereof. Specific examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, maleic acid and fumaric acid. The use of acrylic acid or methacrylic acid is especially preferred. Metal salts of unsaturated carboxylic acids are exemplified by, without particular limitation, the above unsaturated carboxylic acids that have been neutralized with desired metal ions. Specific examples include the zinc salts and magnesium salts of methacrylic acid and acrylic acid. The use of zinc acrylate is especially preferred.

The unsaturated carboxylic acid and/or metal salt thereof is included in an amount, per 100 parts by weight of the base rubber, which is typically at least 15 parts by weight, preferably at least 20 parts by weight, and more preferably at least 25 parts by weight. The amount included is typically not more than 50 parts by weight, preferably not more than 45 parts by weight, and more preferably not more than 40 parts by weight. Too much may make the core too hard, giving the ball an unpleasant feel at impact, whereas too little may lower the rebound.

It is preferable to use an organic peroxide as the crosslinking initiator. Commercial products may be used as the organic peroxide. Examples of such products that may be suitably used include Percumyl D, Perhexa C-40 and Perhexa 3M (all from NOF Corporation), and Luperco 231XL (from AtoChem Co.). One of these may be used alone, or two or more may be used together. The amount of organic peroxide included per 100 parts by weight of the base rubber is preferably at least 0.1 part by weight, more preferably at least 0.3 part by weight, and even more preferably at least 0.5 part by weight. The upper limit is preferably not more than 5 parts by weight, more preferably not more than 4 parts by weight, even more preferably not more than 3 parts by weight, and most preferably not more than 2.5 parts by weight. When too much or too little is included, it may not be possible to obtain a ball having a good feel, durability and rebound.

Fillers that may be suitably used include zinc oxide, barium sulfate and calcium carbonate. These may be used singly or two or more may be used in combination. The amount of filler included per 100 parts by weight of the base rubber may be set to preferably at least 4 parts by weight, more preferably at least 5 parts by weight, and even more preferably at least 7 parts by weight. The upper limit in the amount of filler included per 100 parts by weight of the base rubber may be set to preferably not more than 100 parts by weight, more preferably not more than 75 parts by weight, and even more preferably not more than 50 parts by weight. At a filler content which is too high or too low, a proper weight and a suitable rebound may be impossible to obtain.

Commercial products such as Nocrac NS-6, Nocrac NS-30, Nocrac 200 and Nocrac MB (all products of Ouchi Shinko Chemical Industry Co., Ltd.) may be used as antioxidants. These may be used singly, or two or more may be used in combination.

The amount of antioxidant included per 100 parts by weight of the base rubber, although not particularly limited, is preferably at least 0.05 part by weight, and more preferably at least 0.1 part by weight. The upper limit is preferably not more than 1.0 part by weight, more preferably not more than 0.7 part by weight, and even more preferably not more than 0.5 part by weight. When the antioxidant content is too high or too low, a suitable core hardness gradient may not be obtained, as a result of which it may not be possible to obtain a good rebound, a good durability and a good spin rate-lowering effect on full shots.

In addition, an organosulfur compound may be included in the rubber composition so as to impart an excellent rebound. Thiophenols, thionaphthols, halogenated thiophenols, and metal salts thereof are recommended for this purpose. Illustrative examples include pentachlorothiophenol, pentafluorothiophenol, pentabromothiophenol, p-chlorothiophenol, and the zinc salt of pentachlorothiophenol; and also diphenylpolysulfides, dibenzylpolysulfides, dibenzoylpolysulfides, dibenzothiazoylpolysulfides and dithiobenzoylpolysulfides having 2 to 4 sulfurs. The use of diphenyldisulfide or the zinc salt of pentachlorothiophenol is especially preferred.

The amount of the organosulfur compound included per 100 parts by weight of the base rubber is at least 0.05 part by weight, preferably at least 0.07 part by weight, and more preferably at least 0.1 part by weight. The upper limit is not more than 5 parts by weight, preferably not more than 4 parts by weight, more preferably not more than 3 parts by weight, and most preferably not more than 2 parts by weight. Including too much organosulfur compound may excessively lower the hardness, whereas including too little is unlikely to improve the rebound.

The core can be produced by vulcanizing/curing the rubber composition containing the above respective ingredients. For example, production may be carried out by kneading the composition using a mixer such as a Banbury mixer or a roll mill, compression molding or injection molding the kneaded composition using a core mold, and curing the molded material by suitably heating it at a temperature sufficient for the organic peroxide or co-crosslinking agent to act, i.e., between 100° C. and 200° C., preferably between 140° C. and 180° C., for 10 to 40 minutes.

Next, the hardness profile of the core is described. The hardness of the core refers hereinafter to the Shore C hardness. This Shore C hardness is a hardness value measured with a Shore C durometer in accordance with ASTM D2240.

The core has a center hardness (Cc) which is preferably at least 54, more preferably at least 57, and even more preferably at least 60. The upper limit is preferably not more than 69, more preferably not more than 67, and even more preferably not more than 65. When this value is too large, the feel at impact may harden, or the spin rate on full shots may rise, as a result of which the intended distance may not be achieved. On the other hand, when this value is too small, the rebound may become lower and so a good distance may not be obtained, or the durability to cracking under repeated impact may worsen.

The core has a surface hardness (Cs) which is preferably at least 70, more preferably at least 74, and even more preferably at least 77. The upper limit is preferably not more than 90, more preferably not more than 87, and even more preferably not more than 85. A core surface hardness outside of this range may lead to undesirable results similar to those described above for the core center hardness (Cc).

The core has a hardness Cm at the midpoint between the core surface and core center which, although not particularly limited, may be set to preferably at least 58, more preferably at least 61, and even more preferably at least 64. The upper limit value is preferably not more than 75, more preferably not more than 74, and even more preferably not more than 72. A hardness that deviates from these values may lead to undesirable results similar to those described above for the core center hardness (Cc).

The Shore C hardness value obtained by subtracting the core center hardness (Cc) from the core surface hardness (Cs) is 16 or more, preferably 17 or more, and more preferably 18 or more. The upper limit value is preferably not more than 25, more preferably not more than 22, and even more preferably not more than 21. When this value is too small, the spin rate on full shots with a driver becomes high, as a result of which the desired distance may not be attainable. When this hardness difference is larger than the above range, the durability of the ball to cracking on repeated impact may worsen or the initial velocity on shots may decrease, as a result of which the intended distance may not be attainable. In cases where the above hardness difference is smaller than the above range on account of a large core deflection hardness, the initial velocity of the ball on full shots with a driver is low, as a result of which the desired distance may not be attainable.

With regard to the interior hardness of the core, the value expressed as (Cs−Cm)/(Cm−Cc) is preferably at least 1.5, more preferably at least 1.7, and even more preferably at least 1.9. The upper limit is preferably 10.0 or less, more preferably 8.0 or less, and even more preferably 5.0 or less. When this value is too large, the durability to cracking on repeated impact may worsen or the initial velocity on shots may become low, as a result of which the intended distance may not be attainable. On the other hand, when this value is too small, the spin rate on full shots may rise, as a result of which the intended distance may not be attainable.

Letting the core volume (mm³) multiplied by the Shore C hardness at the midpoint between the core surface and core center be Core vh, the value of Core vh is preferably at least 800, more preferably at least 900, and even more preferably at least 1,000; the upper limit value is preferably 1,540 or less, more preferably 1,480 or less, and even more preferably 1,430 or less. When the Core vh value is too small, the ball initial velocity may decrease and a good distance may not be obtained. On the other hand, when the Core vh value is too large, the spin rate on full shots with an iron may rise and the intended distance may not be attainable.

Next, the envelope layer is described.

In this invention, the envelope layer is formed of two layers: an inner layer and an outer layer. These are referred to as, respectively, the inner envelope layer and the outer envelope layer.

The inner envelope layer has a material hardness on the Shore C hardness scale which, although not particularly limited, is preferably at least 67, more preferably at least 70, and even more preferably at least 72. The upper limit is preferably not more than 90, more preferably not more than 89, and even more preferably not more than 88. The material hardness of the inner envelope layer on the Shore D hardness scale is preferably at least 43, more preferably at least 45, and even more preferably at least 47. The upper limit is preferably not more than 60, more preferably not more than 56, and even more preferably not more than 54.

The sphere obtained by encasing the core with the inner envelope layer (inner envelope layer-encased sphere) has a surface hardness which, on the Shore C hardness scale, is preferably at least 75, more preferably at least 78, and even more preferably at least 80. The upper limit is preferably not more than 94, more preferably not more than 92, and even more preferably not more than 90. The surface hardness on the Shore D hardness scale is preferably at least 49, more preferably at least 51, and even more preferably at least 53. The upper limit is preferably not more than 66, more preferably not more than 62, and even more preferably not more than 60.

When the material hardness and the surface hardness of the inner envelope layer are lower than the above ranges, the ball may be too receptive to spin on full shots or the initial velocity may decline, as a result of which a good distance may not be achieved. On the other hand, when the material hardness and the surface hardness are too high, the feel at impact may become hard, the durability to cracking on repeated impact may worsen, or the spin rate on full shots may rise, as a result of which a good distance may not be achieved.

The surface hardness of the inner envelope layer-encased sphere is higher than the surface hardness of the core. When this is not the case, the spin rate on full shots rises and the intended distance cannot be attained.

The inner envelope layer has a thickness that is preferably at least 0.8 mm, more preferably at least 1.0 mm, and even more preferably at least 1.2 mm. The upper limit in the thickness of the inner envelope layer is preferably 1.8 mm or less, more preferably 1.7 mm or less, and even more preferably 1.6 mm or less. When the inner envelope layer thickness falls outside of this range, the spin rate lowering effect on full shots may be inadequate and a good distance may not be achieved. Also, when the inner envelope layer is too thin, the durability to cracking on repeated impact and the low-temperature durability may worsen.

Letting IE vh be the inner envelope layer volume (mm³) multiplied by the Shore C surface hardness of the inner envelope layer-encased sphere, the value of IE vh is preferably at least 380, more preferably at least 410, and even more preferably at least 440. The upper limit value is preferably 520 or less, more preferably 500 or less, and even more preferably 480 or less. When the IE vh value falls outside of the above range, the spin rate-lowering effect on full shots may be inadequate, as a result of which a good distance may not be achieved.

The value of (OE vh+IE vh)/Core vh, where OE vh and Core vh are as defined below, is preferably at least 0.4, more preferably at least 0.5, and even more preferably at least 0.6. The upper limit is preferably 1.1 or less, more preferably 1.0 or less, and even more preferably 0.9 or less. When this value is too small, the initial velocity on shots may decrease, as a result of which a good distance may not be achieved. On the other hand, when this value is too large, the initial velocity may decrease or the spin rate on full shots may rise, as a result of which the intended distance may not be achieved.

The outer envelope layer has a material hardness on the Shore C hardness scale which is preferably at least 75, more preferably at least 78, and even more preferably at least 80. The upper limit is preferably not more than 95, more preferably not more than 92, and even more preferably not more than 90. The surface hardness of the outer envelope layer on the Shore D hardness scale is preferably at least 46, more preferably at least 48, and even more preferably at least 50. The upper limit is preferably not more than 63, more preferably not more than 59, and even more preferably not more than 57.

The sphere obtained by encasing the inner envelope layer-encased sphere with the outer envelope layer (outer envelope layer-encased sphere) has a surface hardness on the Shore C hardness scale which is preferably at least 83, more preferably at least 86, and even more preferably at least 88. The upper limit is preferably not more than 95, more preferably not more than 93, and even more preferably not more than 92. The surface hardness on the Shore D hardness scale is preferably at least 52, more preferably at least 54, and even more preferably at least 56. The upper limit is preferably not more than 69, more preferably not more than 65, and even more preferably not more than 63.

When the material hardness and the surface hardness of the outer envelope layer are lower than the above ranges, the ball may take on too much spin on full shots or the initial velocity may decrease, as a result of which a good distance may not be achieved. On the other hand, when the material hardness and the surface hardness are too high, the feel at impact may become too hard, the durability to cracking on repeated impact may worsen, or the spin rate on full shots may rise, as a result of which a good distance may not be achieved.

The outer envelope layer has a thickness which is preferably at least 0.7 mm, more preferably at least 0.9 mm, and even more preferably at least 1.1 mm. The upper limit in the thickness of the outer envelope layer is preferably 1.7 mm or less, more preferably 1.6 mm or less, and even more preferably 1.5 mm or less. When the outer envelope layer thickness falls outside of this range, the spin rate-lowering effect on full shots may be inadequate and a good distance may not be achieved. Also, when the outer envelope layer is too thin, the durability to cracking on repeated impact and the low-temperature durability may worsen.

To lower the spin rate of the ball on full shots and increase the distance traveled by the ball, it is critical for the outer envelope layer to have a smaller thickness than the inner envelope layer. The value obtained by subtracting the outer envelope layer thickness from the inner envelope layer thickness is larger than 0 mm, preferably at least 0.1 mm, and more preferably at least 0.2 mm. The upper limit value is generally 0.5 mm or less, preferably 0.4 mm or less, and more preferably 0.3 mm or less. When this value falls outside of the above range, the spin rate on full shots may rise and a good distance may not be achieved.

Letting OE vh the outer envelope layer volume (mm³) multiplied by the Shore C surface hardness of the outer envelope layer-encased sphere, the value of OE vh is preferably at least 380, more preferably at least 410, and even more preferably at least 440. The upper limit value is preferably 600 or less, more preferably 540 or less, and even more preferably 480 or less. When the OE vh value falls outside of the above range, the spin rate-lowering effect on full shots may be inadequate and so a good distance may not be achieved.

The total thickness of the envelope layer is preferably at least 2.0 mm, more preferably at least 2.2 mm, and even more preferably at least 2.4 mm. The upper limit value is preferably not more than 4.0 mm, more preferably not more than 3.5 mm, and even more preferably not more than 3.0 mm. When the total thickness of the envelope layer is too large, the initial velocity may decrease and a good distance may not be achieved. When the overall thickness of the envelope layer is too low, the spin rate-lowering effect may be insufficient and a good distance may not be achieved on full shots with an iron.

The materials making up the inner envelope layer and the outer envelope layer are not particularly limited; known resins may be used for this purpose. Examples of preferred materials include resin compositions containing as the essential ingredients: 100 parts by weight of a resin component composed of, in admixture,

(A) a base resin of (a-1) an olefin-unsaturated carboxylic acid random copolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid random copolymer mixed with (a-2) an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer and/or a metal ion neutralization product of an olefin-unsaturated carboxylic acid-unsaturated carboxylic acid ester random terpolymer in a weight ratio between 100:0 and 0:100, and

(B) a non-ionomeric thermoplastic elastomer in a weight ratio between 100:0 and 50:50;

(C) from 5 to 120 parts by weight of a fatty acid and/or fatty acid derivative having a molecular weight of from 228 to 1,500; and

(D) from 0.1 to 17 parts by weight of a basic inorganic metal compound capable of neutralizing un-neutralized acid groups in components A and C.

Components A to D in the intermediate layer-forming resin material described in, for example, JP-A 2010-253268 may be advantageously used as above components A to D.

The resin materials that form the inner envelope layer and the outer envelope layer may be mutually like or unlike. As subsequently described, in this invention, the outer envelope layer-encased sphere has a higher surface hardness than the inner envelope layer-encased sphere. One way to have the resin material of the outer envelope layer be harder than the resin material of the inner envelope layer is to mix a suitable amount of a relatively hard ionomer resin together with the resin material composed of components (A) to (D) above, thereby forming a resin material for the outer envelope layer which differs from the resin material for the inner envelope layer.

A non-ionomeric thermoplastic elastomer may be included in the respective materials for the inner envelope layer and the outer envelope layer. The non-ionomeric thermoplastic elastomer is preferably included in an amount of from 0 to 50 parts by weight per 100 parts by weight of the total amount of the base resin.

Exemplary non-ionomeric thermoplastic elastomers include polyolefin elastomers (including polyolefins and metallocene polyolefins), polystyrene elastomers, diene polymers, polyacrylate polymers, polyamide elastomers, polyurethane elastomers, polyester elastomers and polyacetals.

Depending on the intended use, optional additives may be suitably included in the above resin materials. For example, pigments, dispersants, antioxidants, ultraviolet absorbers and light stabilizers may be added. When these additives are included, the amount added per 100 parts by weight of the overall base resin is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight. The upper limit is preferably not more than 10 parts by weight, and more preferably not more than 4 parts by weight.

Next, the intermediate layer is described.

The intermediate layer has a material hardness on the Shore D hardness scale which, although not particularly limited, is preferably at least 58, more preferably at least 60, and even more preferably at least 63. The upper limit is preferably not more than 70, more preferably not more than 68, and even more preferably not more than 65. The material hardness on the Shore C hardness scale is preferably at least 87, more preferably at least 89, and even more preferably at least 93. The upper limit is preferably not more than 100, more preferably not more than 98, and even more preferably not more than 96.

The sphere obtained by encasing the outer envelope layer-encased sphere with the intermediate layer (intermediate layer-encased sphere) has a surface hardness on the Shore D hardness scale which is preferably at least 64, more preferably at least 66, and even more preferably at least 69. The upper limit is preferably not more than 76, more preferably not more than 74, and even more preferably not more than 71. The surface hardness on the Shore C hardness scale is preferably at least 90, more preferably at least 93, and even more preferably at least 96. The upper limit is preferably not more than 100, more preferably not more than 99, and even more preferably not more than 98.

When the material hardness and surface hardness of the intermediate layer are lower than the above respective ranges, the ball may take on too much spin on full shots, or the initial velocity may decrease, resulting in a poor distance. On the other hand, when the material hardness and surface hardness are too high, the durability of the ball to cracking on repeated impact may worsen or the feel at impact on shots with a putter and on short approaches may be too hard.

The surface hardness of the intermediate layer-encased sphere is set to a higher value than the surface hardness of the ball and the surface hardness of the outer envelope layer-encased sphere. When this is not the case, the spin rate on full shots will rise, preventing a good distance from being achieved, or the controllability of the ball in the short game will worsen.

The intermediate layer has a thickness of preferably at least 0.7 mm, more preferably at least 0.8 mm, and even more preferably at least 1.0 mm. The upper limit in the intermediate layer thickness is preferably 1.8 mm or less, more preferably 1.4 mm or less, and even more preferably 1.2 mm or less.

The intermediate layer has a greater thickness than the subsequently described cover (outermost layer). The value obtained by subtracting the cover thickness from the intermediate layer thickness is preferably at least 0.04 mm, and more preferably at least 0.08 mm. The upper limit value is preferably 1.5 mm or less, more preferably 1.0 mm or less, and even more preferably 0.6 mm or less. When the cover is thicker than the intermediate layer, the spin rate on full shots may rise or the initial velocity may decrease, which may result in a poor distance. On the other hand, when this value is too large, the ball may not be receptive to spin in the short game or the cover may cut easily when the ball is topped with a wedge.

The intermediate layer material may be suitably selected from among various types of thermoplastic resins that are used as golf ball materials, with the use of the highly neutralized resin material containing components (a) to (c) described above in connection with the envelope layer materials or the use of an ionomer resin being preferred.

Specific examples of ionomer resin materials include high-acid ionomers having an acid content of at least 16 wt %, sodium-neutralized ionomer resins and zinc-neutralized ionomer resins. These may be used singly or two or more may be used together.

An embodiment that uses in admixture a zinc-neutralized ionomer resin and a sodium-neutralized ionomer resin as the chief materials is especially preferred. The blending ratio therebetween, expressed as the weight ratio (zinc-neutralized ionomer)/(sodium-neutralized ionomer), is from 25/75 to 75/25, preferably from 35/65 to 65/35, and more preferably from 45/55 to 55/45. When the zinc-neutralized ionomer and sodium-neutralized ionomer are not included in a ratio within this range, the rebound may become too low, as a result of which the desired distance may not be achieved, the durability to cracking on repeated impact at normal temperatures may worsen, or the durability to cracking at low temperatures (subzero Centigrade) may worsen.

Depending on the intended use, optional additives may be suitably included in the intermediate layer material. For example, pigments, dispersants, antioxidants, ultraviolet absorbers and light stabilizers may be added. When these additives are included, the amount added per 100 parts by weight of the base resin is preferably at least 0.1 part by weight, and more preferably at least 0.5 part by weight. The upper limit is preferably not more than 10 parts by weight, and more preferably not more than 4 parts by weight.

It is desirable to abrade the surface of the intermediate layer in order to increase adhesion of the intermediate layer material with the polyurethane that is preferably used in the subsequently described cover material. In addition, it is desirable to apply a primer (adhesive) to the surface of the intermediate layer following such abrasion treatment or to add an adhesion reinforcing agent to the intermediate layer material.

The intermediate layer material has a specific gravity which is typically less than 1.1, preferably between 0.90 and 1.05, and more preferably between 0.93 and 0.99. Outside of this range, the rebound of the overall ball may decrease and a good distance may not be obtained, or the durability of the ball to cracking on repeated impact may worsen.

Next, the cover (outermost layer) is described.

The cover has a material hardness on the Shore D hardness scale which, although not particularly limited, is preferably at least 35, more preferably at least 40, and even more preferably at least 45. The upper limit is preferably not more than 60, more preferably not more than 55, and even more preferably not more than 50. On the Shore C hardness scale, the material hardness is preferably at least 57, more preferably at least 63, and even more preferably at least 70. The upper limit is preferably not more than 89, more preferably not more than 83, and even more preferably not more than 76.

The surface hardness of the sphere obtained by encasing the intermediate layer-encased sphere with the cover (i.e., the ball), expressed on the Shore D hardness scale, is preferably at least 50, more preferably at least 53, and even more preferably at least 56. The upper limit is preferably not more than 70, more preferably not more than 67, and even more preferably not more than 64. On the Shore C hardness scale, the surface hardness is preferably at least 75, more preferably at least 80, and even more preferably at least 85. The upper limit is preferably not more than 95, more preferably not more than 92, and even more preferably not more than 90.

When the material hardness of the cover and the surface hardness of the ball are too much lower than the above respective ranges, the spin rate of the ball on full shots with an iron may rise and a good distance may not be achieved. On the other hand, when the material hardness of the cover and the surface hardness of the ball are too high, the ball may not be receptive to spin on approach shots or the scuff resistance may worsen.

The cover has a thickness of preferably at least 0.3 mm, more preferably at least 0.45 mm, and even more preferably at least 0.6 mm. The upper limit in the cover thickness is preferably not more than 1.2 mm, more preferably not more than 1.15 mm, and even more preferably not more than 1.0 mm. The cover thickness is preferably lower than the intermediate layer thickness. When the cover thickness falls outside of the above range or is greater than the intermediate layer thickness, the ball rebound on full shots with an iron may be inadequate or the spin rate may rise, as a result of which a good distance may not be achieved. On the other hand, when the cover is too thin, the scuff resistance may worsen, or the ball may not be receptive to spin on approach shots, resulting in an inadequate controllability.

Various types of thermoplastic resins and thermoset resins employed as cover stock in golf balls may be used as the cover material. For reasons having to do with ball controllability and scuff resistance, preferred use can be made of a urethane resin. In particular, from the standpoint of the mass productivity of the manufactured balls, it is preferable to use a material that is composed primarily of a thermoplastic polyurethane, and especially preferable to form the cover of a resin blend in which the main components are (I) a thermoplastic urethane and (II) a polyisocyanate compound.

It is recommended that the total weight of components (I) and (II) combined be at least 60%, and preferably at least 70%, of the overall amount of the cover-forming resin blend. Components (I) and (II) are described below.

The thermoplastic polyurethane (I) has a structure which includes soft segments composed of a polymeric polyol (polymeric glycol) that is a long-chain polyol, and hard segments composed of a chain extender and a polyisocyanate compound. Here, the long-chain polyol serving as a starting material may be any that has hitherto been used in the art relating to thermoplastic polyurethanes, and is not particularly limited. Illustrative examples include polyester polyols, polyether polyols, polycarbonate polyols, polyester polycarbonate polyols, polyolefin polyols, conjugated diene polymer-based polyols, castor oil-based polyols, silicone-based polyols and vinyl polymer-based polyols. These long-chain polyols may be used singly, or two or more may be used in combination. Of these, in terms of being able to synthesize a thermoplastic polyurethane having a high rebound resilience and excellent low-temperature properties, a polyether polyol is preferred.

Any chain extender that has hitherto been employed in the art relating to thermoplastic polyurethanes may be suitably used as the chain extender. For example, low-molecular-weight compounds with a molecular weight of 400 or less which have on the molecule two or more active hydrogen atoms capable of reacting with isocyanate groups are preferred. Illustrative, non-limiting, examples of the chain extender include 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. Of these, the chain extender is preferably an aliphatic diol having 2 to 12 carbon atoms, and more preferably 1,4-butylene glycol.

Any polyisocyanate compound hitherto employed in the art relating to thermoplastic polyurethanes may be suitably used without particular limitation as the polyisocyanate compound. For example, use may be made of one or more selected from the group consisting of 4,4′-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, trimethylhexamethylene diisocyanate and dimer acid diisocyanate. However, depending on the type of isocyanate, the crosslinking reactions during injection molding may be difficult to control. In the practice of the invention, to provide a balance between stability at the time of production and the properties that are manifested, it is most preferable to use the following aromatic diisocyanate: 4,4′-diphenylmethane diisocyanate.

Commercially available products may be used as the thermoplastic polyurethane serving as component (I). Illustrative examples include Pandex T-8295, Pandex T-8290 and Pandex T-8260 (all from DIC Covestro Polymer, Ltd.).

A thermoplastic elastomer other than the above thermoplastic polyurethanes may also be optionally included as a separate component, i.e., component (III), together with above components (I) and (II). By including this component (III) in the above resin blend, the flowability of the resin blend can be further improved and properties required of the golf ball cover material, such as resilience and scuff resistance, can be increased.

The compositional ratio of above components (I), (II) and (III) is not particularly limited. However, to fully elicit the advantageous effects of the invention, the compositional ratio (I):(II):(III) is preferably in the weight ratio range of from 100:2:50 to 100:50:0, and more preferably from 100:2:50 to 100:30:8.

In addition, various additives other than the ingredients making up the above thermoplastic polyurethane may be optionally included in this resin blend. For example, pigments, dispersants, antioxidants, light stabilizers, ultraviolet absorbers and internal mold lubricants may be suitably included.

The manufacture of multi-piece solid golf balls in which the above-described core, inner envelope layer, outer envelope layer, intermediate layer and cover (outermost layer) are formed as successive layers may be carried out by a customary method such as a known injection molding process. For example, a multi-piece golf ball can be produced by successively injection-molding the respective materials for the inner envelope layer, outer envelope layer and intermediate layer over the core in injection molds for each layer so as to obtain the respective layer-encased spheres and then, last of all, injection-molding the material for the cover serving as the outermost layer over the intermediate layer-encased sphere. Alternatively, the encasing layers may each be formed by enclosing the sphere to be encased within two half-cups that have been pre-molded into hemispherical shapes and then molding under applied heat and pressure.

The golf ball has a deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) which is preferably at least 1.8 mm, more preferably at least 2.0 mm, and even more preferably at least 2.2 mm. The upper limit value is preferably not more than 3.0 mm, more preferably not more than 2.7 mm, and even more preferably not more than 2.5 mm. When the ball deflection is too small, i.e., when the ball is too hard, the spin rate of the ball may rise excessively so that the ball does not achieve a good distance, or the feel at impact may be too hard. On the other hand, when the ball deflection is too large, i.e., when the ball is too soft, the ball rebound may become so low that the ball does not achieve a good distance, the feel at impact may be too soft, or the durability to cracking under repeated impact may worsen.

Hardness Relationships Among Layers

In this invention, it is critical for the surface hardness of the core, the surface hardness of the sphere obtained by encasing the core with the inner envelope layer (inner envelope layer-encased sphere), the surface hardness of the sphere obtained by encasing the inner envelope layer-encased sphere with the outer envelope layer (outer envelope layer-encased sphere), the surface hardness of the sphere obtained by encasing the outer envelope layer-encased sphere with the intermediate layer (intermediate layer-encased sphere) and the surface hardness of the ball to satisfy the following relationship in which the hardnesses are Shore C hardness values:

-   -   core surface hardness<surface hardness of inner envelope         layer-encased sphere<surface hardness of outer envelope         layer-encased sphere<surface hardness of intermediate         layer-encased sphere>ball surface hardness.         By satisfying this hardness relationship, a satisfactory         distance can be achieved on full shots with a driver (W#1) or an         iron, in addition to which the ball is highly receptive to spin         on approach shots and thus superior in the short game.

The Shore C hardness value obtained by subtracting the core surface hardness from the surface hardness of the inner envelope layer-encased sphere is more than 0, preferably 2 or more, and more preferably 4 or more. The upper limit is preferably not more than 20, more preferably not more than 16, and even more preferably not more than 13. When this value is too small, the initial velocity of the ball is low and a good distance is not achieved. When this value is too large, the durability to cracking on repeated impact may worsen.

The Shore C hardness value obtained by subtracting the core center hardness from the surface hardness of the outer envelope layer-encased sphere is preferably 23 or more, more preferably 25 or more, and even more preferably 27 or more. The upper limit is preferably not more than 40, more preferably not more than 35, and even more preferably not more than 32. When this value is too small, the spin rate on full shots may rise and a good distance may not be achieved. When this value is too large, the initial velocity on shots may decrease and a good distance may not be achieved, or the durability to cracking under repeated impact may worsen.

The Shore C hardness value obtained by subtracting the core surface hardness from the surface hardness of the outer envelope layer-encased sphere is preferably 5 or more, more preferably 6 or more, and even more preferably 7 or more. The upper limit is preferably not more than 28, more preferably not more than 23, and even more preferably not more than 20. When this value is too small, the spin rate on full shots may rise and a good distance may not be achieved. When this value is too large, the initial velocity on shots may decrease and a good distance may not be achieved, or the durability to cracking under repeated impact may worsen.

The Shore C hardness value obtained by subtracting the surface hardness of the inner envelope layer-encased sphere from the surface hardness of the outer envelope layer-encased sphere is more than 0, preferably 2 or more, and more preferably 3 or more. The upper limit is preferably not more than 16, more preferably not more than 14, and even more preferably not more than 12. When this value is too small, the spin rate on full shots rises and a good distance cannot be achieved. When this value is too large, the initial velocity on shots may become low and a good distance may not be achieved.

The Shore C hardness value obtained by subtracting the surface hardness of the outer envelope layer-encased sphere from the surface hardness of the intermediate layer-encased sphere is more than 0, preferably 2 or more, and more preferably 4 or more. The upper limit is preferably not more than 18, more preferably not more than 15, and even more preferably not more than 12. When this value is too small, the spin rate on full shots rises and a good distance cannot be achieved. When this value is too large, the initial velocity on shots may become low and a good distance may not be achieved.

The Shore C hardness value obtained by subtracting the core center hardness from the surface hardness of the intermediate layer-encased sphere is preferably 30 or more, more preferably 32 or more, and even more preferably 34 or more. The upper limit is preferably not more than 45, more preferably not more than 43, and even more preferably not more than 40. When this value is too small, the spin rate on full shots may rise and a good distance may not be achieved. When this value is too large, the initial velocity on shots may decrease and a good distance may not be achieved, or the durability to cracking on repeated impact may worsen.

The Shore C hardness value obtained by subtracting the ball surface hardness from the surface hardness of the intermediate layer-encased sphere is more than 0, preferably 2 or more, and more preferably 4 or more. The upper limit is preferably not more than 20, more preferably not more than 17, and even more preferably not more than 14. When this value is too small, i.e., when the ball surface is harder than the intermediate layer surface, the ball is not sufficiently receptive to spin in the short game (this being the case especially when the cover is hard) or the spin rate on full shots rises, as a result of which a good distance is not achieved (this being the case especially when the intermediate layer is soft). On the other hand, when the above value is too large, the spin rate on full shots may rise, as a result of which a good distance is not achieved (this being the case especially when the cover is too soft) or the durability to cracking on repeated impact may worsen (this being the case especially when the intermediate layer is too hard).

Other Relationships Among Layers

The value obtained by dividing the overall thickness of the envelope layer by the combined thickness of the cover and the intermediate layer, which value is expressed as [(overall thickness of envelope layer)/(intermediate layer thickness+cover thickness)], is preferably at least 0.8, more preferably at least 0.9, and even more preferably at least 1.0. The upper limit value is preferably 1.6 or less, more preferably 1.4 or less, and even more preferably 1.2 or less. When this value is too large, the initial velocity may decrease, as a result of which a good distance may not be achieved, or the durability to cracking on repeated impact may worsen. On the other hand, when this value is too small, the spin rate-lowering effect may be inadequate, as a result of which a good distance may not be achieved.

The core diameter/ball diameter value is preferably at least 0.702, more preferably at least 0.735, and even more preferably at least 0.749. The upper limit value is preferably 0.821 or less, more preferably 0.802 or less, and even more preferably 0.785 or less. When this value is too small, the initial velocity of the ball may decrease, as a result of which a good distance may not be achieved. On the other hand, when this value is too large, the spin rate on full shots with an iron may rise, as a result of which the intended distance may not be achieved.

Letting S and B the deflections in millimeters of, respectively, the core and the ball when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf), the value B−S, although not particularly limited, is preferably at least 0.8 mm, more preferably at least 0.9 mm, and even more preferably at least 1.0 mm. The upper limit value is preferably 3.3 mm or less, more preferably 2.7 mm or less, and even more preferably 2.2 mm or less. When this value is too small, the spin rate on full shots may rise and so a good distance may not be achieved. On the other hand, when this value is too large, the initial velocity on shots may be low and so a good distance may not be achieved, or the durability to cracking on repeated impact may worsen.

Numerous dimples may be formed on the surface of the cover serving as the outermost layer. The number of dimples arranged on the cover surface, although not particularly limited, is preferably at least 323, more preferably at least 326, and even more preferably at least 330. The upper limit is preferably not more than 380, more preferably not more than 360, and even more preferably not more than 350. When the number of dimples is higher than this range, the ball trajectory may become lower and the distance traveled by the ball may decrease. On the other hand, when the number of dimples is lower that this range, the ball trajectory may become higher and a good distance may not be achieved.

The dimple shapes used may be of one type or may be a combination of two or more types suitably selected from among, for example, circular shapes, various polygonal shapes, dewdrop shapes and oval shapes. When circular dimples are used, the dimple diameter may be set to at least about 2.5 mm and up to about 6.5 mm, and the dimple depth may be set to at least 0.08 mm and up to 0.30 mm.

In order for the aerodynamic properties to be fully manifested, it is desirable for the dimple coverage ratio on the spherical surface of the golf ball, i.e., the dimple surface coverage SR, which is the sum of the individual dimple surface areas, each defined by the flat plane circumscribed by the edge of a dimple, as a percentage of the spherical surface area of the ball were the ball to have no dimples thereon, to be set to at least 70% and not more than 90%. Also, to optimize the ball trajectory, it is desirable for the value V₀, defined as the spatial volume of the individual dimples below the flat plane circumscribed by the dimple edge, divided by the volume of the cylinder whose base is the flat plane and whose height is the maximum depth of the dimple from the base, to be set to at least 0.35 and not more than 0.80. Moreover, it is preferable for the ratio VR of the sum of the volumes of the individual dimples, each formed below the flat plane circumscribed by the edge of the dimple, with respect to the volume of the ball sphere were the ball surface to have no dimples thereon, to be set to at least 0.6% and not more than 1.0%. Outside of the above ranges in these respective values, the resulting trajectory may not enable a good distance to be achieved and so the ball may fail to travel a fully satisfactory distance.

It is desirable for the golf ball of the invention to optimize the ratios CL2/CL1 and CL4/CL3, where CL1 is the coefficient of lift at a Reynolds number of 80,000 and a spin rate of 2,000 rpm, CL2 is the coefficient of lift at a Reynolds number of 70,000 and a spin rate of 1,900 rpm, CL3 is the coefficient of lift at a Reynolds number of 200,000 and a spin rate of 2,500 rpm and CL4 is the coefficient of lift at a Reynolds number of 120,000 and a spin rate of 2,250 rpm.

In this Specification, the coefficients of lift (CL1, CL2, CL3 and CL4) are measured in conformity with the Indoor Test Range (ITR) method established by the United States Golf Association (USGA). The coefficient of lift can be adjusted by adjusting the golf ball dimple configuration (arrangement, diameter, depth, volume, number, shape, etc.). The coefficient of lift does not depend on the internal construction of the golf ball. The Reynolds number (Re) is a dimensionless number used in the field of fluid dynamics, and is computed using formula (I) below.

Re=ρvL/μ  (I)

In formula (I), ρ represents the density of a fluid, v is the relative average velocity of an object relative to flow by the fluid, L is a characteristic length, and μ is the coefficient of viscosity of the fluid.

The conditions under which the coefficient of lift CL1 is measured, i.e., a Reynolds number of 80,000 and a spin rate of 2,000 rpm, generally correspond approximately to the state at the time that the coefficient of lift begins to decrease and, in turn, the golf ball begins to fall after having reached its highest point following launch. The conditions under which the coefficient of lift CL2 is measured, i.e., a Reynolds number of 70,000 and a spin rate of 1,900 rpm, generally correspond approximately to the state just before the golf ball falls to the ground after having reached its highest point following launch. The above is particularly true in cases where the golf ball is launched under high-velocity conditions (e.g., an initial velocity of 66 m/s, a spin rate of 2,600 rpm, and a launch angle of 11°). These high-velocity conditions generally correspond to the launch conditions when the ball is hit with a driver by an amateur golfer.

The ratio CL2/CL1 has a value of preferably at least 0.900, more preferably at least 0.970, and even more preferably at least 0.990. By satisfying the above range, the decrease in lift as the golf ball falls can be suppressed, which in turn makes it easier for the flight distance (i.e., the carry) to be extended as the ball falls and for the run to be extended. Hence, the total distance can be increased. When CL2/CL1 is too low, the golf ball tends to fall more abruptly, making it difficult to satisfactorily increase the carry and run. A higher CL2/CL1 is better from the standpoint of increasing the total distance. However, when this value is too high, the carry is extended but the run decreases, as a result of which the total distance may not exceed the optimal value. Therefore, the upper limit value for CL2/CL1 is 1.100 or less, preferably 1.018 or less, more preferably 0.999 or less, and even more preferably 0.995 or less.

The conditions under which the coefficient of lift CL3 is measured, i.e. a Reynolds number of 200,000 and a spin rate of 2,500 rpm, generally correspond approximately to the state just after the golf ball has been launched under high-velocity conditions (e.g., an initial velocity of 72 m/s, a spin rate of 2,500 rpm and a launch angle of 10°). The conditions under which the coefficient of lift CL4 is measured, i.e. a Reynolds number of 120,000 and a spin rate of 2,250 rpm, generally correspond approximately to the state when approximately 2 seconds have elapsed as the ball rises after being launched under high-velocity conditions (e.g., an initial velocity of 72 m/s, a spin rate of 2,500 rpm and a launch angle of 10°).

The ratio CL4/CL3 has a value of preferably at least 1.250, more preferably at least 1.252, and even more preferably at least 1.255. The upper limit is preferably not more than 1.300, more preferably not more than 1.295, and even more preferably not more than 1.290. By setting the ratio in this range, when the golf ball has been launched under high-velocity conditions (e.g., when hit with a driver), the amount of rise by the golf ball can be kept from becoming excessive (i.e., the ball can be kept from climbing too steeply), making it possible to increase the resistance of the ball to wind and thus enabling the carry to be increased. In addition, the run can be increased. This enables the total distance traveled by the ball to be increased.

From the standpoint of increasing the distance traveled by the ball, the coefficient of lift CL1 is preferably at least 0.230. Also, CL1 is preferably not more than 0.240. From the same standpoint, the coefficient of lift CL2 is preferably at least 0.230. Also, CL2 is preferably not more than 0.240. From the same standpoint, the coefficient of lift CL3 is preferably at least 0.145. Also, CL3 is preferably not more than 0.155. From the same standpoint, the coefficient of lift CL4 is preferably at least 0.185. Also, CL4 is preferably not more than 0.195.

A coating layer may be formed on the surface of the cover. This coating layer can be formed by applying various types of coating materials. Because the coating layer must be capable of enduring the harsh conditions of golf ball use, it is desirable to use a coating composition in which the chief component is a urethane coating material composed of a polyol and a polyisocyanate.

The polyol component is exemplified by acrylic polyols and polyester polyols. These polyols include modified polyols. To further increase workability, other polyols may also be added.

It is suitable to use two types of polyester polyol together as the polyol component. In this case, letting the two types of polyester polyol be component (a) and component (b), a polyester polyol in which a cyclic structure has been introduced onto the resin skeleton may be used as the polyester polyol of component (a). Examples include polyester polyols obtained by the polycondensation of a polyol having an alicyclic structure, such as cyclohexane dimethanol, with a polybasic acid; and polyester polyols obtained by the polycondensation of a polyol having an alicyclic structure with a diol or triol and a polybasic acid. A polyester polyol having a branched structure may be used as the polyester polyol of component (b). Examples include polyester polyols having a branched structure, such as NIPPOLAN 800, from Tosoh Corporation.

The polyisocyanate is exemplified without particular limitation by commonly used aromatic, aliphatic, alicyclic and other polyisocyanates. Specific examples include tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, 1,4-cyclohexylene diisocyanate, naphthalene diisocyanate, trimethylhexamethylene diisocyanate, dicyclohexylmethane diisocyanate and 1-isocyanato-3,3,5-trimethyl-4-isocyanatomethylcyclohexane. These may be used singly or in admixture.

Depending on the coating conditions, various types of organic solvents may be mixed into the coating composition. Examples of such organic solvents include aromatic solvents such as toluene, xylene and ethylbenzene; ester solvents such as ethyl acetate, butyl acetate, propylene glycol methyl ether acetate and propylene glycol methyl ether propionate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ether solvents such as diethylene glycol dimethyl ether, diethylene glycol diethyl ether and dipropylene glycol dimethyl ether; alicyclic hydrocarbon solvents such as cyclohexane, methyl cyclohexane and ethyl cyclohexane; and petroleum hydrocarbon solvents such as mineral spirits.

The thickness of the coating layer made of the coating composition, although not particularly limited, is typically from 5 to 40 μm, and preferably from 10 to 20 μm. As used herein, “coating layer thickness” refers to the coating thickness obtained by averaging the measurements taken at a total of three places: the center of a dimple and two places located at positions between the dimple center and the dimple edge.

In this invention, the coating layer composed of the above coating composition has an elastic work recovery that is preferably at least 60%, and more preferably at least 80%. At a coating layer elastic work recovery in this range, the coating layer has a high elasticity and so the self-repairing ability is high, resulting in an outstanding abrasion resistance. Moreover, the performance attributes of golf balls coated with this coating composition can be improved. The method of measuring the elastic work recovery is described below.

The elastic work recovery is one parameter of the nanoindentation method for evaluating the physical properties of coating layers, this being a nanohardness test method that controls the indentation load on a micro-newton (μN) order and tracks the indenter depth during indentation to a nanometer (nm) precision. In prior methods, only the size of the deformation (plastic deformation) mark corresponding to the maximum load could be measured. However, in the nanoindentation method, the relationship between the indentation load and the indentation depth can be obtained by continuous automated measurement. Hence, unlike in the past, there are no individual differences between observers when visually measuring a deformation mark under an optical microscope, and so it is thought that the physical properties of the coating layer can be precisely evaluated. Given that the coating layer on the ball surface is strongly affected by the impact of drivers and various other types of clubs, and has a not inconsiderable influence on various golf ball properties, measuring the coating layer by the nanohardness test method and carrying out such measurement to a higher precision than in the past is a very effective method of evaluation.

The hardness of the coating layer, as expressed on the Shore M hardness scale, is preferably at least 40, and more preferably at least 60. The upper limit is preferably not more than 95, and more preferably not more than 85. This Shore M hardness is obtained in accordance with ASTM D2240. The hardness of the coating layer, as expressed on the Shore C hardness scale, is preferably at least 40, and more preferably at least 50; the upper limit is preferably not more than 80, and more preferably not more than 70. This Shore C hardness is obtained in accordance with ASTM D2240. At coating layer hardnesses that are higher than these ranges, the coating may become brittle when the ball is repeatedly struck, which may make it incapable of protecting the cover layer. On the other hand, coating layer hardnesses that are lower than the above range are undesirable because the ball surface is more easily damaged when striking a hard object.

When the above coating composition is used, the formation of a coating layer on the surface of golf balls manufactured by a known method can be carried out via the steps of preparing the coating composition at the time of application, applying the composition onto the golf ball surface by a conventional coating operation, and drying the applied composition. The coating technique is not particularly limited. For example, spray painting, electrostatic painting or dipping may be suitably used.

The multi-piece solid golf ball of the invention can be made to conform to the Rules of Golf for play. The inventive ball may be formed to a diameter which is such that the ball does not pass through a ring having an inner diameter of 42.672 mm and is not more than 42.80 mm, and to a weight which is preferably between 45.0 and 45.93 g.

EXAMPLES

The following Examples and Comparative Examples are provided to illustrate the invention, and are not intended to limit the scope thereof.

Of Examples 1 to 4 according to the invention and Comparative Examples 1 to 18 below, Comparative Examples 7 to 14 are predictive data that can be inferred from measured values obtained in the other Examples of the invention and Comparative Examples and are not Examples that were actually carried out. These Comparative Examples 7 to 14 are treated below in the same way as the other Examples and Comparative Examples.

Examples 1 to 4, Comparative Examples 1 to 18

Formation of Core

Solid cores were produced by preparing rubber compositions for the respective Examples and Comparative Examples shown in Tables 1 and 2, and then vulcanizing the compositions for 15 minutes at 155° C.

TABLE 1 Core formulation Example Comparative Example (pbw) 1 2 3 4 1 2 3 4 5 6 Polybutadiene (I) 100 100 100 100 100 100 100 100 100 100 Zinc acrylate 38.0 34.0 31.0 28.0 31.5 26.0 21.0 31.5 26.0 21.0 Organic peroxide 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 Sulfur Zinc stearate 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 Zinc oxide 32.5 33.9 35.0 47.9 76.2 77.1 78.1 76.2 77.1 78.1 Zinc salt of 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 pentachlorothiophenol

TABLE 2 Core formulation Comparative Example (pbw) 7 8 9 10 11 12 13 14 15 16 17 18 Polybutadiene (I) 100 100 100 100 100 100 100 100 100 100 100 80 Polybutadiene (II) 20 Zinc acrylate 33.0 23.0 31.0 21.0 28.0 33.0 33.0 39.0 41.0 37.0 32.0 35.0 Organic peroxide 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2 3.0 Sulfur 0.1 Zinc stearate 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 Antioxidant 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0 Zinc oxide 46.3 49.4 35.1 50.0 58.2 46.3 46.3 44.6 25.8 27.3 29.3 21.9 Zinc salt of 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 1.5 pentachlorothiophenol

Details on the ingredients mentioned in Tables 1 and 2 are given below.

-   -   Polybutadiene (I): Available under the trade name “BR 730” from         JSR Corporation     -   Polybutadiene (II): Available under the trade name “BR 51” from         JSR Corporation     -   Zinc acrylate: “ZN-DA85S” from Nippon Shokubai Co., Ltd.     -   Organic Peroxide: A mixture of 1,1-Di(t-butylperoxy)cyclohexane         and silica, available under the trade name “Perhexa C-40” from         NOF Corporation     -   Zinc stearate: Available as “Zinc Stearate G” from NOF         Corporation     -   Antioxidant: 2,2′-Methylenebis(4-methyl-6-butylphenol),         available under the trade name “Nocrac NS-6” from Ouchi Shinko         Chemical Industry Co., Ltd.     -   Zinc oxide: Available as “Grade 3 Zinc Oxide” from Sakai         Chemical Co., Ltd.     -   Zinc salt of pentachlorothiophenol: Available from Wako Pure         Chemical Industries, Ltd.

Formation of Inner and Outer Envelope Layers

Next, in each Example and Comparative Example, an inner envelope layer was formed by injection-molding the inner envelope layer material shown in Table 3 over the core, following which an outer envelope layer was formed by injection-molding the outer envelope layer material shown in the same table over the inner envelope layer. In Comparative Examples 15 to 17, the material of formulation No. 2 in Table 3 was injection-molded over the core to form a single envelope layer (the details are provided in the “Outer envelope layer” section in the table). No envelope layer was formed in Comparative Example 18.

Formation of Intermediate Layer and Cover (Outermost Layer)

Next, in all of the working Examples and Comparative Examples except for Comparative Example 18, an intermediate layer was formed by injection-molding the intermediate layer material shown in Table 3 over the envelope layer-encased sphere obtained above. A cover (outermost layer) was then formed by injection-molding the cover material shown in the same table over the resulting intermediate layer-encased sphere. A plurality of given dimples common to all the Examples and Comparative Examples were formed at this time on the surface of the cover.

TABLE 3 Resin composition (pbw) No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 HPF 1000 100 Himilan 1601 50 Himilan 1605 68.75 50 Himilan 1557 50 15 Himilan 1706 35 AM 7315 50 AM 7318 50 Dynaron 6100P 31.25 Behenic acid 18 20 Calcium hydroxide 2.3 2.8 Calcium stearate 0.15 Zinc stearate 0.15 Trimethylolpropane 1.1 Polytail H 2 Titanium oxide 4 TPU 100

Trade names for the materials in the above table are given below.

-   -   HPF 1000: Available under the trademark Dow™ from The Dow         Chemical Company     -   Himilan: Ionomers available from Dow-Mitsui Polychemicals Co.,         Ltd.     -   AM 7315, AM 7318: Ionomers available from Dow-Mitsui         Polychemicals Co., Ltd.     -   Dynaron 6100P: A hydrogenated polymer available from JSR         Corporation     -   Behenic acid: NAA222-S (beads) from NOF Corporation     -   Calcium hydroxide: Available as “CLS-B” from Shiraishi Calcium         Kaisha, Ltd.     -   Trimethylolpropane (TMP): Available from Tokyo Chemical Industry         Co., Ltd.     -   Polytail™ H: Product name for a polyhydroxy hydrocarbon polymer         from Mitsubishi Chemical Corporation     -   TPU: An ether-type thermoplastic polyurethane (Shore D hardness         of material, 48) available as Pandex® from DIC Covestro Polymer,         Ltd.

Eight types of circular dimples were used as the dimples D. Details on the dimples are shown in Table 4 below, and the dimple pattern is shown in FIG. 2. FIG. 2A is a top view of a golf ball on the surface of which the dimples D have been formed, and FIG. 2B is a side view of the same.

TABLE 4 Dimples Diameter Depth Volume Cylinder SR VR D Number (mm) (mm) (mm³) volume ratio (%) (%) D-1 12 4.6 0.123 1.116 0.546 82.30 0.775 D-2 198 4.45 0.122 1.036 0.546 D-3 36 3.85 0.119 0.757 0.546 D-4 12 2.75 0.090 0.288 0.539 D-5 36 4.45 0.136 1.120 0.530 D-6 24 3.85 0.133 0.820 0.530 D-7 6 3.4 0.118 0.563 0.526 D-8 6 3.3 0.118 0.530 0.525 Total 330

Dimple Definitions

-   -   Edge: Highest place in cross-section passing through center of         dimple.     -   Diameter: Diameter of flat plane circumscribed by edge of         dimple.     -   Depth: Maximum depth of dimple from flat plane circumscribed by         edge of dimple.     -   SR: Sum of individual dimple surface areas, each defined by flat         plane circumscribed by edge of dimple, as a percentage of         spherical surface area of ball were it to have no dimples         thereon.     -   Dimple volume: Dimple volume below flat plane circumscribed by         edge of dimple.     -   Cylinder volume ratio: Ratio of dimple volume to volume of         cylinder having same diameter and depth as dimple.     -   VR: Sum of volumes of individual dimples formed below flat plane         circumscribed by edge of dimple, as a percentage of volume of         ball sphere were it to have no dimples thereon.

For the golf balls having Dimples D formed on the surface of the cover, the coefficient of lift CL1 measured at a Reynolds number of 80,000 and a spin rate of 2,000 rpm, the coefficient of lift CL2 measured at a Reynolds number of 70,000 and a spin rate of 1,900 rpm, the coefficient of lift CL3 measured at a Reynolds number of 200,000 and a spin rate of 2,500 rpm, the coefficient of lift CL4 measured at a Reynolds number of 120,000 and a spin rate of 2,250 rpm, and the values of the ratios CL2/CL1 and CL4/CL3 are shown in Table 5 below. These coefficients of lift were measured in conformity with the Indoor Test Range (ITR) method established by the United States Golf Association (USGA).

TABLE 5 CL1 CL2 CL3 CL4 CL2/CL1 CL4/CL3 Dimples D 0.234 0.238 0.148 0.186 1.018 1.262

Formation of Coating Layer

Next, using Coating Composition C shown in Table 6 below as a coating composition common to all of the Examples and Comparative Examples, the coating was applied with an air spray gun onto the surface of the cover (outermost layer) having numerous dimples formed thereon, producing golf balls with a 15 μm-thick coating layer on top.

TABLE 6 Coating composition Base resin Polyester polyol (A) 23 (parts by weight) Polyester polyol (B) 15 Organic solvent 62 Curing agent Isocyanate (HMDI 42 isocyanurate) Solvent 58 Molar blending ratio (NCO/OH) 0.89 Coating properties Elastic work recovery (%) 84 Shore M hardness 84 Shore C hardness 63 Thickness (μm) 15

Synthesis of Polyester Polyol (A)

A reactor equipped with a reflux condenser, a dropping funnel, a gas inlet and a thermometer was charged with 140 parts by weight of trimethylolpropane, 95 parts by weight of ethylene glycol, 157 parts by weight of adipic acid and 58 parts by weight of 1,4-cyclohexanedimethanol, following which the reaction was effected by raising the temperature to between 200 and 240° C. under stirring and heating for 5 hours. This yielded Polyester Polyol (A) having an acid value of 4, a hydroxyl value of 170 and a weight-average molecular weight (Mw) of 28,000.

The Polyester Polyol (A) thus synthesized was then dissolved in butyl acetate, thereby preparing a varnish having a nonvolatiles content of 70 wt %.

The base resin for the coating composition in Table 6 was prepared by mixing together 23 parts by weight of the above polyester polyol solution, 15 parts by weight of Polyester Polyol (B) (the saturated aliphatic polyester polyol NIPPOLAN 800 from Tosoh Corporation; weight-average molecular weight (Mw), 1,000; 100% solids) and the organic solvent. This mixture had a nonvolatiles content of 38.0 wt %.

Elastic Work Recovery

The elastic work recovery of the coating material was measured using a coating sheet having a thickness of 50 μm. The ENT-2100 nanohardness tester from Erionix Inc. was used as the measurement apparatus, and the measurement conditions were as follows.

-   -   Indenter: Berkovich indenter (material: diamond; angle α:         65.03°)     -   Load F: 0.2 mN     -   Loading time: 10 seconds     -   Holding time: 1 second     -   Unloading time: 10 seconds

The elastic work recovery was calculated as follows, based on the indentation work W_(elast) (Nm) due to spring-back deformation of the coating and on the mechanical indentation work W_(total) (Nm).

Elastic work recovery=W _(elast) /W _(total)×100 (%)

Shore C Hardness and Shore M Hardness

The Shore C hardness and Shore M hardness in Table 6 above were determined by forming the material being tested into 2 mm thick sheets and stacking three such sheets together to give test specimens. Measurements were taken using a Shore C durometer and a Shore M durometer in accordance with ASTM D2240.

Various properties of the resulting golf balls, including the internal hardnesses of the core at various positions, the diameters of the core and each layer-encased sphere, the thickness and material hardness of each layer, and the surface hardness of each layer-encased sphere, were evaluated by the following methods. The results are presented in Tables 7 to 10.

Diameters of Core, Inner Envelope Layer-Encased Sphere, Outer Envelope Layer-Encased Sphere, and Intermediate Layer-Encased Sphere

The diameters at five random places on the surface were measured at a temperature of 23.9±1° C. and, using the average of these measurements as the measured value for a single core, envelope layer-encased sphere or intermediate layer-encased sphere, the average diameter for ten such spheres were determined.

Ball Diameter

The diameter at 15 random dimple-free areas was measured at a temperature of 23.9±1° C. and, using the average of these measurements as the measured value for a single ball, the average diameter for ten balls was determined.

Deflections of Core, Inner Envelope Layer-Encased Sphere, Outer Envelope Layer-Encased Sphere, Intermediate Laver-Encased Sphere and Ball

The sphere to be measured (i.e., a core, inner envelope layer-encased sphere, outer envelope layer-encased sphere, intermediate layer-encased sphere or ball) was placed on a hard plate and the amount of deflection when compressed under a final load of 1,275 N (130 kgf) from an initial load of 98 N (10 kgf) was measured. The amount of deflection refers in each case to the measured value obtained after holding the core isothermally at 23.9° C.

Core Hardness Profile

The indenter of a durometer was set substantially perpendicular to the spherical surface of the core, and the surface hardness on the Shore C hardness scale was measured in accordance with ASTM D2240. The P2 Automatic Rubber Hardness Tester (Kobunshi Keiki Co., Ltd.) equipped with a Shore C durometer can be used for measuring the hardness. The maximum value is read off as the hardness value. Measurements were all carried out in a 23±2° C. environment. The core center hardness Cc and the hardness Cm at the midpoint between the core center and core surface were measured by perpendicularly pressing the indenter of a durometer against the positions to be measured on the flat cross-section obtained by cutting the core into hemispheres. The results are indicated as Shore C hardness values.

Material Hardnesses (Shore C and Shore D) of Inner Envelope Layer, Outer Envelope Layer, Intermediate Layer and Cover

The resin material for each layer was molded into a sheet having a thickness of 2 mm and left to stand for at least two weeks at a temperature of 23±2° C. Three sheets were stacked together at the time of measurement. The Shore C hardness and Shore D hardness of each material were measured with a Shore C durometer and a Shore D durometer in accordance with ASTM D2240. The P2 Automatic Rubber Hardness Tester (Kobunshi Keiki Co., Ltd.) having a Shore C durometer or Shoe D durometer mounted thereon can be used for measuring the hardness. The maximum value is read off as the hardness value.

Surface Hardnesses (Shore C and Shore D) of Inner Envelope Layer-Encased Sphere, Outer Envelope Layer-Encased Sphere, Intermediate Layer-Encased Sphere and Ball

These hardnesses were measured by perpendicularly pressing an indenter against the surfaces of the respective spheres. The surface hardness of a ball (cover) is the value measured at a dimple-free area (land) on the surface of the ball. The P2 Automatic Rubber Hardness Tester (Kobunshi Keiki Co., Ltd.) having a Shore C durometer or Shore D durometer mounted thereon can be used for measuring the hardness. The maximum value is read off as the hardness value.

TABLE 7 Example Comparative Example 1 2 3 4 1 Construction (piece) 5P 5P 5P 5P 5P Core Diameter (mm) 33.50 33.42 33.53 31.43 27.76 Weight (g) 24.55 24.30 24.70 21.33 16.59 Volume (mm³) 19.68 19.55 19.74 16.26 11.20 Deflection (mm) 3.2 3.6 4.1 4.4 3.9 Hardness Core surface hardness: Cs 85 83 79 77 81 profile Hardness at midpoint between 72 70 67 65 68 (Shore C) core surface and center: Cm Core center hardness: Cc 65 63 61 60 62 Core surface hardness − 20 19 18 17 19 Core center hardness (Cs − Cm)/(Cm − Cc) 1.9 1.9 2.0 2.0 1.9 Core volume × 1421 1370 1330 1065 765 Hardness at midpoint between core surface and center Inner Material No. 1 No. 1 No. 1 No. 1 No. 1 envelope Thickness (mm) 1.37 1.40 1.35 1.46 2.26 layer Volume (mm³) 5.24 5.34 5.17 4.98 6.41 Material hardness (Shore C) 84 84 84 84 84 Material hardness (Shore D) 52 52 52 52 52 Inner Diameter (mm) 36.24 36.22 36.24 34.36 32.28 envelope Weight (g) 29.62 29.51 29.60 26.18 22.47 layer-encased Deflection (mm) 2.9 3.3 3.8 4.1 3.1 sphere Surface hardness (Shore C) 89 89 89 89 89 Surface hardness (Shore D) 57 57 57 57 57 Surface hardness of inner envelope layer − 4 6 10 12 8 Core surface hardness (Shore C) Volume of inner envelope layer × Surface hardness of 466 475 460 444 570 inner envelope layer-encased sphere (Shore C) Outer Material No. 2 No. 2 No. 2 No. 2 No. 2 envelope Thickness (mm) 1.10 1.10 1.10 1.37 1.94 layer Volume (mm³) 4.80 4.81 4.81 5.52 7.16 Material hardness (Shore C) 87 87 87 87 87 Material hardness (Shore D) 56 56 56 56 56 Overall thickness of envelope layer (mm) 2.47 2.50 2.45 2.84 4.20 Inner envelope layer thickness − 0.27 0.30 0.25 0.09 0.32 Outer envelope layer thickness (mm) Outer Diameter (mm) 38.43 38.42 38.44 37.11 36.16 envelope Weight (g) 34.08 34.02 34.12 31.28 29.29 layer-encased Deflection (mm) 2.7 3.0 3.4 3.6 3.0 sphere Material hardness (Shore C) 92 92 92 92 92 Material hardness (Shore D) 62 62 62 62 62 Outer envelope layer surface hardness − 27 29 31 32 30 Core center hardness (Shore C) Outer envelope layer hardness − 7 9 13 15 11 Core surface hardness (Shore C) Outer envelope layer surface hardness − 3 3 3 3 3 Inner envelope layer surface hardness (Shore C) Outer envelope layer volume × Surface hardness 442 443 443 508 658 of outer envelope layer-encased sphere (Shore C) Comparative Example 2 3 4 5 6 Construction (piece) 5P 5P 5P 5P 5P Core Diameter (mm) 27.71 27.70 27.76 27.71 27.70 Weight (g) 16.56 16.58 16.59 16.56 16.58 Volume (mm³) 11.14 11.13 11.20 11.14 11.13 Deflection (mm) 4.6 5.5 3.9 4.6 5.5 Hardness Core surface hardness: Cs 75 70 81 75 70 profile Hardness at midpoint between 64 59 68 64 59 (Shore C) core surface and center: Cm Core center hardness: Cc 59 55 62 59 55 Core surface hardness − 17 15 19 17 15 Core center hardness (Cs − Cm)/(Cm − Cc) 2.0 2.2 1.9 2.0 2.2 Core volume × 715 660 765 715 660 Hardness at midpoint between core surface and center Inner Material No. 1 No. 1 No. 2 No. 2 No. 2 envelope Thickness (mm) 2.28 2.29 2.24 2.27 2.28 layer Volume (mm³) 6.46 6.47 6.35 6.42 6.44 Material hardness (Shore C) 84 84 87 87 87 Material hardness (Shore D) 52 52 56 56 56 Inner Diameter (mm) 32.28 32.28 32.24 32.25 32.26 envelope Weight (g) 22.48 22.48 22.57 22.57 22.59 layer-encased Deflection (mm) 3.7 4.4 3.5 4.2 5.0 sphere Surface hardness (Shore C) 89 89 92 92 92 Surface hardness (Shore D) 57 57 62 62 62 Surface hardness of inner envelope layer − 14 19 11 17 22 Core surface hardness (Shore C) Volume of inner envelope layer × Surface hardness of 575 576 584 591 592 inner envelope layer-encased sphere (Shore C) Outer Material No. 2 No. 2 No. 3 No. 3 No. 3 envelope Thickness (mm) 1.95 1.95 1.96 1.96 1.96 layer Volume (mm³) 7.20 7.18 7.22 7.20 7.22 Material hardness (Shore C) 87 87 91 91 91 Material hardness (Shore D) 56 56 60 60 60 Overall thickness of envelope layer (mm) 4.24 4.23 4.21 4.23 4.24 Inner envelope layer thickness − 0.33 0.34 0.28 0.32 0.31 Outer envelope layer thickness (mm) Outer Diameter (mm) 36.18 36.17 36.17 36.16 36.18 envelope Weight (g) 29.31 29.30 29.31 29.35 29.33 layer-encased Deflection (mm) 3.4 3.9 2.3 2.6 2.9 sphere Material hardness (Shore C) 92 92 95 95 95 Material hardness (Shore D) 62 62 66 66 66 Outer envelope layer surface hardness − 33 37 33 36 40 Core center hardness (Shore C) Outer envelope layer hardness − 17 22 14 20 25 Core surface hardness (Shore C) Outer envelope layer surface hardness − 3 3 3 3 3 Inner envelope layer surface hardness (Shore C) Outer envelope layer volume × Surface hardness 662 660 686 684 686 of outer envelope layer-encased sphere (Shore C)

TABLE 8 Comparative Example 7 8 9 10 11 12 Construction (piece) 5P 5P 5P 5P 5P 5P Core Diameter (mm) 31.42 31.43 33.14 31.43 31.43 31.42 Weight (g) 21.38 21.45 23.89 21.45 22.23 21.38 Volume (mm³) 16.24 16.25 19.06 16.25 16.26 16.24 Deflection (mm) 3.7 5.3 4.1 5.8 4.4 3.7 Hardness Core surface hardness: Cs 82 71 79 67 77 82 profile Hardness at midpoint between 69 60 67 58 65 69 (Shore C) core surface and center: Cm Core center hardness: Cc 63 55 61 53 60 63 Core surface hardness − 19 15 18 14 17 19 Core center hardness (Cs − Cm)/(Cm − Cc) 1.9 2.2 2.0 2.3 2.0 1.9 Core volume × 1125 978 1284 936 1065 1125 Hardness at midpoint between core surface and center Inner Material No. 1 No. 1 No. 1 No. 1 No. 1 No. 1 envelope Thickness (mm) 1.38 1.38 1.35 1.47 1.46 1.47 layer Volume (mm³) 4.65 4.66 5.06 4.99 4.98 5.02 Material hardness (Shore C) 84 84 84 84 84 84 Material hardness (Shore D) 52 52 52 52 52 52 Inner Diameter (mm) 34.17 34.18 35.85 34.36 34.36 34.37 envelope Weight (g) 25.69 25.75 28.67 26.20 27.08 26.18 layer-encased Deflection (mm) 3.5 5.2 3.8 5.6 4.1 3.4 sphere Surface hardness (Shore C) 89 89 89 89 89 89 Surface hardness (Shore D) 57 57 57 57 57 57 Surface hardness of inner envelope layer − 7 18 10 22 12 7 Core surface hardness (Shore C) Volume of inner envelope layer × Surface hardness of 414 415 450 444 444 446 inner envelope layer-encased sphere (Shore C) Outer Material No. 2 No. 2 No. 2 No. 2 No. 2 No. 4 envelope Thickness (mm) 1.47 1.47 1.10 1.38 1.37 1.38 layer Volume (mm³) 5.89 5.86 4.71 5.53 5.52 5.53 Material hardness (Shore C) 87 87 87 87 87 92 Material hardness (Shore D) 56 56 56 56 56 62 Overall thickness of envelope layer (mm) 2.85 2.84 2.45 2.84 2.84 2.85 Inner envelope layer thickness − −0.10 −0.09 0.25 0.09 0.09 0.10 Outer envelope layer thickness (mm) Outer Diameter (mm) 37.12 37.11 38.04 37.11 37.11 37.12 envelope Weight (g) 31.29 31.31 33.10 31.31 32.18 31.29 layer-encased Deflection (mm) 3.0 4.2 3.4 4.7 3.6 3.0 sphere Material hardness (Shore C) 92 92 92 92 92 95 Material hardness (Shore D) 62 62 62 62 62 64 Outer envelope layer surface hardness − 29 37 31 39 32 32 Core center hardness (Shore C) Outer envelope layer hardness − 10 21 13 25 15 13 Core surface hardness (Shore C) Outer envelope layer surface hardness − 3 3 3 3 3 6 Inner envelope layer surface hardness (Shore C) Outer envelope layer volume × Surface hardness 542 539 434 509 508 525 of outer envelope layer-encased sphere (Shore C) Comparative Example 13 14 15 16 17 18 Construction (piece) 5P 5P 4P 4P 4P 3P Core Diameter (mm) 31.42 31.42 35.08 35.07 35.12 37.18 Weight (g) 21.38 21.38 27.57 27.42 27.72 31.67 Volume (mm³) 16.24 16.24 22.60 22.58 22.68 26.91 Deflection (mm) 3.7 2.7 3.1 3.4 3.9 3.7 Hardness Core surface hardness: Cs 82 89 86 84 80 84 profile Hardness at midpoint between 69 75 73 71 68 71 (Shore C) core surface and center: Cm Core center hardness: Cc 63 67 66 64 62 62 Core surface hardness − 19 21 20 20 18 22 Core center hardness (Cs − Cm)/(Cm − Cc) 1.9 1.8 1.9 1.9 1.9 1.4 Core volume × 1125 1218 1641 1608 1544 1921 Hardness at midpoint between core surface and center Inner Material No. 2 No. 1 envelope Thickness (mm) 1.47 1.47 layer Volume (mm³) 5.02 5.02 Material hardness (Shore C) 87 84 Material hardness (Shore D) 56 52 Inner Diameter (mm) 34.37 34.37 envelope Weight (g) 26.18 26.18 layer-encased Deflection (mm) 3.3 2.4 sphere Surface hardness (Shore C) 87 89 Surface hardness (Shore D) 56 57 Surface hardness of inner envelope layer − 5 0 Core surface hardness (Shore C) Volume of inner envelope layer × Surface hardness of 436 446 inner envelope layer-encased sphere (Shore C) Outer Material No. 1 No. 2 No. 2 No. 2 No. 2 envelope Thickness (mm) 1.38 1.38 1.59 1.59 1.57 layer Volume (mm³) 5.53 5.53 6.73 6.73 6.62 Material hardness (Shore C) 84 87 87 87 87 Material hardness (Shore D) 52 56 56 56 56 Overall thickness of envelope layer (mm) 2.85 2.85 1.59 1.59 1.57 Inner envelope layer thickness − 0.10 0.10 — — — Outer envelope layer thickness (mm) Outer Diameter (mm) 37.12 37.12 38.26 38.25 38.25 envelope Weight (g) 31.29 31.29 33.85 33.79 33.90 layer-encased Deflection (mm) 3.1 2.6 2.8 2.9 3.4 sphere Material hardness (Shore C) 84 92 92 92 92 Material hardness (Shore D) 52 62 62 62 62 Outer envelope layer surface hardness − 21 25 26 28 30 Core center hardness (Shore C) Outer envelope layer hardness − 2 3 6 8 12 Core surface hardness (Shore C) Outer envelope layer surface hardness − −3 3 — — — Inner envelope layer surface hardness (Shore C) Outer envelope layer volume × Surface hardness 462 509 620 619 609 of outer envelope layer-encased sphere (Shore C)

TABLE 9 Example Comparative Example 1 2 3 4 1 2 3 4 5 6 Intermediate Material No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 layer Thickness (mm) 1.09 1.12 1.11 1.78 2.24 2.22 2.23 2.23 2.23 2.22 Material hardness (Shore C) 95 95 95 95 95 95 95 95 95 95 Material hardness (Shore D) 64 64 64 64 64 64 64 64 64 64 Intermediate Diameter (mm) 40.62 40.67 40.65 40.67 40.64 40.62 40.62 40.63 40.63 40.62 layer-encased Weight (g) 39.14 39.16 39.20 39.29 39.11 39.04 39.05 39.12 39.12 39.09 sphere Deflection (mm) 2.4 2.6 2.8 2.6 2.0 2.2 2.4 1.6 1.7 1.8 Surface hardness (Shore C) 97 97 97 97 97 97 97 97 97 97 Surface hardness (Shore D) 70 70 70 70 70 70 70 70 70 70 Intermediate layer surface hardness − 5 5 5 5 5 5 5 2 2 2 Outer envelope layer surface hardness (Shore C) Intermediate layer surface hardness − 32 34 36 37 35 38 42 35 38 42 Core center hardness (Shore C) Cover Material No. 5 No. 5 No. 5 No. 5 No. 5 No. 5 No. 5 No. 5 No. 5 No. 5 Thickness (mm) 1.01 0.99 1.00 0.99 1.01 1.02 1.02 1.02 1.01 1.01 Material hardness (Shore C) 74 74 74 74 74 74 74 74 74 74 Material hardness (Shore D) 48 48 48 48 48 48 48 48 48 48 Coating Material C C C C C C C C C C Material hardness (Shore C) 63 63 63 63 63 63 63 63 63 63 Dimples Type D D D D D D D D D D Number 330 330 330 330 330 330 330 330 330 330 Ball Diameter (mm) 42.65 42.65 42.66 42.65 42.66 42.66 42.67 42.67 42.66 42.65 Weight (g) 45.11 45.07 45.20 45.17 45.08 45.04 45.06 45.06 45.03 45.05 Deflection (mm) 2.2 2.3 2.5 2.3 1.8 1.9 2.0 1.5 1.6 1.6 Surface hardness (Shore C) 90 90 90 90 90 90 90 90 90 90 Surface hardness (Shore D) 59 59 59 59 59 59 59 59 59 59 Intermediate layer thickness − Cover thickness (mm) 0.08 0.13 0.10 0.79 1.22 1.20 1.20 1.21 1.22 1.21 Overall thickness of envelope layer/ 1.17 1.18 1.16 1.02 1.29 1.31 1.30 1.29 1.30 1.31 (Cover thickness + Intermediate layer thickness) Core diameter/Ball diameter 0.785 0.784 0.786 0.737 0.651 0.650 0.649 0.651 0.650 0.650 Intermediate layer surface hardness − 7 7 7 7 7 7 7 7 7 7 Ball surface hardness (Shore C) Core deflection − Ball deflection (mm) 1.0 1.3 1.5 2.1 2.1 2.7 3.5 2.4 3.1 3.9 (OE vh + IE vh)/Core vh 0.64 0.67 0.68 0.89 1.61 1.73 1.87 1.66 1.78 1.94

TABLE 10 Comparative Example 7 8 9 10 11 12 Intermediate Material No. 4 No. 4 No. 4 No. 4 No. 4 No. 2 layer Thickness (mm) 1.74 1.78 1.11 1.78 1.78 1.74 Material hardness (Shore C) 95 95 95 95 95 92 Material hardness (Shore D) 64 64 64 64 64 62 Intermediate Diameter (mm) 40.61 40.68 40.26 40.68 40.67 40.61 layer-encased Weight (g) 39.14 39.37 38.13 39.37 40.19 39.14 sphere Deflection (mm) 2.3 2.8 2.8 3.1 2.6 2.4 Surface hardness (Shore C) 97 97 97 97 97 92 Surface hardness (Shore D) 70 70 70 70 70 62 Intermediate layer surface hardness − 5 5 5 5 5 −3 Outer envelope layer surface hardness (Shore C) Intermediate layer surface hardness − 34 42 36 44 37 29 Core center hardness (Shore C) Cover Material No. 5 No. 5 No. 5 No. 5 No. 6 No. 5 Thickness (mm) 1.02 0.99 1.20 0.99 0.99 1.02 Material hardness (Shore C) 74 74 74 74 98 74 Material hardness (Shore D) 48 48 48 48 68 48 Coating Material C C C C C C Material hardness (Shore C) 63 63 63 63 63 63 Dimples Type D D D D D D Number 330 330 330 330 330 330 Ball Diameter (mm) 42.65 42.66 42.66 42.66 42.65 42.65 Weight (g) 45.17 45.18 45.20 45.18 45.20 45.17 Deflection (mm) 2.1 2.5 2.5 2.6 1.9 2.2 Surface hardness (Shore C) 90 90 90 90 100 90 Surface hardness (Shore D) 59 59 58 59 74 58 Intermediate layer thickness − 0.73 0.79 −0.09 0.79 0.79 0.72 Cover thickness (mm) Overall thickness of envelope layer/ 1.03 1.03 1.06 1.03 1.03 1.03 (Cover thickness + Intermediate layer thickness) Core diameter/Ball diameter 0.737 0.737 0.777 0.737 0.737 0.737 Intermediate layer surface hardness − 7 7 7 7 −3 2 Ball surface hardness (Shore C) Core deflection − Ball deflection (mm) 1.6 2.8 1.5 3.2 2.5 1.6 (OE vh + IE vh)/Core vh 0.85 0.98 0.69 1.02 0.89 0.86 Comparative Example 13 14 15 16 17 18 Intermediate Material No. 4 No. 4 No. 4 No. 4 No. 4 No. 4 layer Thickness (mm) 1.74 1.74 1.20 1.20 1.21 1.74 Material hardness (Shore C) 95 95 95 95 95 95 Material hardness (Shore D) 64 64 64 64 64 64 Intermediate Diameter (mm) 40.61 40.61 40.67 40.65 40.68 40.66 layer-encased Weight (g) 39.14 39.14 39.41 39.25 39.47 39.50 sphere Deflection (mm) 2.4 2.2 2.3 2.5 2.9 2.9 Surface hardness (Shore C) 97 97 97 97 97 97 Surface hardness (Shore D) 70 70 70 70 70. 70 Intermediate layer surface hardness − 13 5 5 5 5 — Outer envelope layer surface hardness (Shore C) Intermediate layer surface hardness − 34 30 31 33 35 35 Core center hardness (Shore C) Cover Material No. 5 No. 5 No. 5 No. 5 No. 5 No. 5 Thickness (mm) 1.02 1.02 1.00 1.01 0.99 1.01 Material hardness (Shore C) 74 74 74 74 74 74 Material hardness (Shore D) 48 48 48 48 48 48 Coating Material C C C C C C Material hardness (Shore C) 63 63 63 63 63 63 Dimples Type D D D D D D Number 330 330 330 330 330 330 Ball Diameter (mm) 42.65 42.65 42.68 42.67 42.66 42.67 Weight (g) 45.17 45.17 45.28 45.20 45.30 45.40 Deflection (mm) 2.1 1.9 2.1 2.2 2.5 2.6 Surface hardness (Shore C) 90 90 90 90 90 90 Surface hardness (Shore D) 59 59 59 59 59 59 Intermediate layer thickness − 0.73 0.73 0.20 0.19 0.22 0.73 Cover thickness (mm) Overall thickness of envelope layer/ 1.03 1.03 0.72 0.72 0.71 — (Cover thickness + Intermediate layer thickness) Core diameter/Ball diameter 0.737 0.737 0.822 0.822 0.823 0.871 Intermediate layer surface hardness − 7 7 7 7 7 7 Ball surface hardness (Shore C) Core deflection − Ball deflection (mm) 1.6 0.9 1.0 1.1 1.4 1.1 (OE vh + IE vh)/Core vh 0.80 0.78 0.38 0.38 0.39 —

The flight performance of each golf ball on shots with a driver (W#1) and on shots with a number six iron (I#6) and the spin rate on approach shots were evaluated by the following methods. The results are shown in Tables 11 and 12.

Flight Performance (W#1)

-   -   (1) A driver (W#1) was mounted on a golf swing robot and the         distance traveled by the ball when struck at a head speed of 47         m/s was measured and rated according to the criteria shown         below. The club used was the TOUR B XD-5 (loft angle, 9.5°)         manufactured by Bridgestone Sports Co., Ltd. In addition, the         spin rate was measured with a launch monitor immediately after         the ball was similarly struck.         -   Rating Criteria             -   Good: Total distance was at least 233.0 m             -   NG: Total distance was less than 233.0 m     -   (2) The distance traveled by the ball when struck by a similar         driver at a head speed of 42 m/s was measured and rated         according to the criteria shown below.         -   Rating Criteria             -   Good: Total distance was at least 208.0 m             -   NG: Total distance was less than 208.0 m

Flight Performance (I#6)

-   -   (1) A middle iron (I#6) was mounted on a golf swing robot and         the distance traveled by the ball when struck at a head speed of         43 m/s was measured and rated according to the criteria shown         below. The club used was the TOUR B X-CB manufactured by         Bridgestone Sports Co., Ltd. In addition, the spin rate was         measured with a launch monitor immediately after the ball was         similarly struck.         -   Rating Criteria             -   Good: Total distance was at least 164.0 m             -   NG: Total distance was less than 164.0 m

Evaluation of Spin Rate on Approach Shots

A sand wedge (SW) was mounted on a golf swing robot and the amount of spin by the ball when struck at a head speed of 16 m/s was rated according to the criteria shown below. The spin rate was measured with a launch monitor immediately after the ball was struck. The sand wedge used was the Tour B XW-1 manufactured by Bridgestone Sports Co., Ltd.

-   -   Rating Criteria:         -   Good: Spin rate was 5,300 rpm or more         -   NG: Spin rate was less than 5,300 rpm

TABLE 11 Example Comparative Example 1 2 3 4 1 Flight (W#1) Spin rate (rpm) 2,851 2,777 2,671 2,749 2,981 HS = 47 m/s Total distance (m)    235.0    236.1    235.9    233.8    233.6 Rating good good good good good Flight (W#1) Spin rate (rpm) 2,612 2,535 2,467 2,591 2,755 HS = 42 m/s Total distance (m)    210.3    211.8    209.5    209.4    203.4 Rating good good good good NG Flight (I#6) Spin rate (rpm) 6,421 6,223 5,875 6,091 6,780 HS = 43 m/s Total distance (m)    164.4    165.6    165.5    166.0    160.7 Rating good good good good NG Controllability Spin rate (rpm) 5,616 5,540 5,453 5,625 5,694 on approach Rating good good good good good shots Comparative Example 2 3 4 5 6 Flight (W#1) Spin rate (rpm) 2,911 2,864 3,133 3,050 3,052 HS = 47 m/s Total distance (m)   232.1   232.3   230.5   229.0   228.9 Rating NG NG NG NG NG Flight (W#1) Spin rate (rpm) 2,660 2,703 2,889 2,865 2,817 HS = 42 m/s Total distance (m)   204.8   204.0   203.9   205.8   202.4 Rating NG NG NG NG NG Flight (I#6) Spin rate (rpm) 6,482 6,396 7,125 6,931 6,885 HS = 43 m/s Total distance (m)   159.9   160.9   156.3   156.5   158.9 Rating NG NG NG NG NG Controllability Spin rate (rpm) 5,694 5,717 5,874 5,785 5,811 on approach Rating good good good good good shots

TABLE 12 Comparative Example 7 8 9 10 11 12 Flight (W#1) Spin rate (rpm) 2,894 2,670 2,719 2,585 2,560 2,864 HS = 47 m/s Total distance (m)   234.3   232.9   232.9   232.8   237.1   234.7 Rating good NG NG NG good good Flight (W#1) Spin rate (rpm) 2,676 2,458 2,522 2,384 2,411 2,646 HS = 42 m/s Total distance (m)   207.8   206.1   207.5   205.7   213.2   207.9 Rating NG NG NG NG good NG Flight (I#6) Spin rate (rpm) 6,402 5,803 5,878 5,675 5,661 6,398 HS = 43 m/s Total distance (m)   160.1   166.4   165.0   166.9   172.0   160.5 Rating NG good good good good NG Controllability Spin rate (rpm) 5,633 5,544 5,465 5,528 4,650 5,622 on Approach Rating good good good good NG good shots Comparative Example 13 14 15 16 17 18 Flight (W#1) Spin rate (rpm) 2,874 2,994 2,857 2,755 2,631 2,569 HS = 47 m/s Total distance (m)   234.5   235.4   235.0   235.3   235.0   232.4 Rating good good good good good NG Flight (W#1) Spin rate (rpm) 2,651 2,799 2,623 2,619 2,507 2,482 HS = 42 m/s Total distance (m)   208.2   210.1   207.3   206.0   206.5   207.5 Rating good good NG NG NG NG Flight (I#6) Spin rate (rpm) 6,413 6,749 6,418 6,246 5,808 5,817 HS = 43 m/s Total distance (m)   160.0   157.7   165.9   163.3   167.4   165.9 Rating NG NG good NG good good Controllability Spin rate (rpm) 5,635 5,701 5,564 5,537 5,503 5,394 on Approach Rating good good good good good good shots

As demonstrated by the results in the above tables, the golf balls of Comparative Examples 1 to 18 are inferior in the following respects to the golf balls according to the present invention that are obtained in Examples 1 to 4.

In Comparative Example 1, the core diameter is smaller than 30 mm and the ball initial velocity is low. As a result, the distances traveled by the ball on full shots with a driver (W#1) and with an iron are both poor.

In Comparative Example 2, the core diameter is smaller than 30 mm and the ball initial velocity is low. As a result, the distances traveled by the ball on full shots with a driver (W#1) and with an iron are both poor.

In Comparative Example 3, the core diameter is smaller than 30 mm and the ball initial velocity is low, in addition to which the Shore C hardness value obtained by subtracting the core center hardness from the core surface hardness is smaller than 16. As a result, the distances traveled by the ball on full shots with a driver (W#1) and with an iron are both poor.

In Comparative Example 4, the core diameter is smaller than 30 mm and the ball initial velocity is low. As a result, the distances traveled by the ball on full shots with a driver (W#1) and with an iron are both poor.

In Comparative Example 5, the core diameter is smaller than 30 mm and the ball initial velocity is low. As a result, the distances traveled by the ball on full shots with a driver (W#1) and with an iron are both poor.

In Comparative Example 6, the core diameter is smaller than 30 mm and the ball initial velocity is low, in addition to which the Shore C hardness value obtained by subtracting the core center hardness from the core surface hardness is smaller than 16. As a result, the distances traveled by the ball on full shots with a driver (W#1) and with an iron are both poor.

In Comparative Example 7, (thickness of outer envelope layer)≥(thickness of inner envelope layer). As a result, the spin rate of the ball is high and the distances traveled by the ball on full shots with a driver (W#1) and with an iron are both poor.

In Comparative Example 8, (thickness of outer envelope layer) (thickness of inner envelope layer). As a result, the initial velocity of the ball when struck is low and the distance traveled by the ball on shots with a driver (W#1) is poor.

In Comparative Example 9, (cover thickness)≥(intermediate layer thickness). As a result, the spin rate of the ball is high and the ball has a low initial velocity, resulting in a poor distance on shots with a driver (W#1).

In Comparative Example 10, the Shore C hardness value obtained by subtracting the core center hardness from the core surface hardness is lower than 16 and the ball has a low initial velocity when struck. As a result, the distance traveled by the ball on shots with a driver (W#1) is poor.

In Comparative Example 11, (surface hardness of ball)≥(surface hardness of intermediate layer-encased sphere). As a result, the spin rate on approach shots in the short game is insufficient.

In Comparative Example 12, (surface hardness of intermediate layer-encased sphere) (surface hardness of outer envelope layer-encased sphere). As a result, the spin rate on full shots is high and the distances traveled on shots with a driver (W#1) and an iron are poor.

In Comparative Example 13, (surface hardness of outer envelope layer-encased sphere)≤(surface hardness of inner envelope layer-encased sphere). As a result, the spin rate on full shots with an iron is high and the distance traveled is poor.

In Comparative Example 14, (surface hardness of inner envelope layer-encased sphere)≤(surface hardness of core). As a result, the spin rate on full shots is high and the distance traveled on shots with an iron is poor.

The ball in Comparative Example 15 is a four-piece ball (4-layer construction). As a result, the initial velocity when struck is low and the distance traveled by the ball on shots with a driver (W#1) is poor.

The ball in Comparative Example 16 is a four-piece ball (4-layer construction). As a result, the initial velocity when struck is low and the distance traveled by the ball on shots with a driver (W#1) is poor.

The ball in Comparative Example 17 is a four-piece ball (4-layer construction). As a result, the initial velocity when struck is low and the distance traveled by the ball on shots with a driver (W#1) is poor. The ball in Comparative Example 18 is a three-piece ball (3-layer construction).

As a result, the initial velocity when struck is low and the distance traveled by the ball on shots with a driver (W#1) is poor.

Japanese Patent Application No. 2021-035283 is incorporated herein by reference.

Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims. 

1. A multi-piece solid golf ball comprising a core, an envelope layer, an intermediate layer and a cover, wherein the core is formed primarily of a base rubber as one or more layer; the core as a whole has a diameter of at least 30 mm; the envelope layer is formed as two layers—an inner envelope layer and an outer envelope layer; the intermediate layer and the cover are each formed as single layers of a resin material; the core has a surface hardness, the sphere obtained by encasing the core with the inner envelope layer (inner envelope layer-encased sphere) has a surface hardness, the sphere obtained by encasing the inner envelope layer-encased sphere with the outer envelope layer (outer envelope layer-encased sphere) has a surface hardness, the sphere obtained by encasing the outer envelope layer-encased sphere with the intermediate layer (intermediate layer-encased sphere) has a surface hardness and the ball has a surface hardness which together satisfy the following condition in which the hardnesses are Shore C hardness values: core surface hardness<surface hardness of inner envelope layer-encased sphere<surface hardness of outer envelope layer-encased sphere<surface hardness of intermediate layer-encased sphere>ball surface hardness; the Shore C hardness value obtained by subtracting the core center hardness from the core surface hardness is 16 or more; and the envelope layer, the intermediate layer and the cover have respective thicknesses which satisfy the following two conditions: cover thickness<intermediate layer thickness, and outer envelope layer thickness<inner envelope layer thickness.
 2. The golf ball of claim 1, wherein the core center hardness (Cc), core surface hardness (Cs) and the hardness at a midpoint between the core surface and the core center (Cm) satisfy the condition: (Cs−Cm)/(Cm−Cc)≥1.5.
 3. The golf ball of claim 1 which satisfies the condition: 0.4≤(OE vh+IE vh)/Core vh≤1.1, wherein Core vh is the volume (mm³) of the core multiplied by the Shore C hardness at a midpoint between the core surface and the core center (Cm), IE vh is the volume (mm³) of the inner envelope layer multiplied by the Shore C hardness at the surface of the inner envelope layer-encased sphere, and OE vh is the volume (mm³) of the outer envelope layer multiplied by the Shore C hardness at the surface of the outer envelope layer-encased sphere.
 4. The golf ball of claim 1 wherein, letting CL1 be the coefficient of lift at a Reynolds number of 80,000 and a spin rate of 2,000 rpm and CL2 be the coefficient of lift at a Reynolds number of 70,000 and a spin rate of 1,900 rpm, the ball satisfies the following condition: 0.900≤CL2/CL1.
 5. The golf ball of claim 1 wherein, letting CL3 be the coefficient of lift at a Reynolds number of 200,000 and a spin rate of 2,500 rpm and CL4 be the coefficient of lift at a Reynolds number of 120,000 and a spin rate of 2,250 rpm, the ball satisfies the following condition: 1.250≤CL4/CL3≤1.300.
 6. The golf ball of claim 1, wherein the cover has a surface with from 323 to 380 dimples arranged thereon. 